Geomechanical modeling of ultradeep fault‐controlled carbonate reservoirs and its application, a case of the Fuman Oilfield in Tarim Basin

To improve the development efficiency of ultradeep fault‐controlled carbonate reservoirs, the deformation and connectivity mechanism of fractures was revealed through large‐scale rock mechanical experiments. The in situ stress field and fracture activity distribution law of fault‐control carbonate reservoirs were clarified through geomechanical modeling. It is revealed that the fracture activity in different directions and the connectivity of the fracture and cavity in different parts are significantly different, the development effect of different well trajectories is analyzed, and the integrated working method of geological engineering is proposed to scientifically guide the well trajectory design and water injection scheme optimization. The results show that: (1) Large‐scale fractures and high‐angle fracture systems in the deformation of strike–slip faults are the key factors affecting reservoir quality. High‐pressure water injection can activate preexisting fractures, and it can extend on the basis of preexisting fractures, and even generate new fractures, which promote the interconnection of fault‐controlled fracture‐cave bodies in the vertical and horizontal directions. (2) During the process of high‐pressure water injection, the coupling change between mechanics and flow occurs inside the fracture body, the seepage environment is improved, and the oil and gas recovery factor is improved through cyclic lifting. (3) According to the shape and occurrence of the fault body and the dynamic shear deformation connectivity of the fault surface, the best well point and well trajectory of the directional well can be optimized, and the water injection scheme can be optimized. (4) The single‐well production increased by 1.45 × 104 t through high‐pressure water injection, the cumulative oil increase of the same fracture‐cavity body increased by 4.63 × 104 t. This method is highly efficient for ultradeep fault‐controlled oil reservoirs. The development provides a good theoretical basis and technical support, and plays a leading and exemplary role.


| INTRODUCTION
The Ordovician carbonate rocks in the Tarim Basin are rich in hydrocarbon resources, which is a key area for increasing oil and gas reserves and production in the Tarim Basin.2][3][4] In recent years, with the increasing degree of oil and gas exploration of Ordovician carbonate rocks in the paleouplift and slope, it began to enter the Amun Loliang (Shuntuogole Low-uplift) area and obtained major oil and gas exploration breakthroughs.6][7] These reservoirs are controlled by the strike-slip fault in the large craton, with oil column heights greater than 550 m and oil production of over 1000 t from a single well, featuring high and stable production, and a scale of 1 billion tons of oil resources has been implemented. 8he exploration and development of carbonate reservoirs related to strike-slip fractures have become a hot spot.][16][17] With the deepening of exploration and development, the development of this type of reservoir also faces the problem of large variations in single-well production capacity caused by strong inhomogeneity, and research on the fluid flow mode inside the special seam space under deep burial conditions is still weak.Research on how to improve the recovery rate in the middle and later stages of development is still unclear, and the lack of quantitative prediction methods for the connectivity of the seam body restricts the long-term large-scale and efficient development of this type of reservoir.
To improve the development efficiency of ultradeep fracture-controlled carbonate reservoirs, this paper reveals the deformation and connectivity mechanism of high-angle-near-erect fracture surfaces by conducting mechanical experiments on large-size rock samples and clarifies the distribution rules of the in situ stress field and fracture activity of fracture-controlled carbonate reservoirs through geomechanical modeling based on the coupling principle of mechanics and flow of highpressure water injection and extraction.There are significant differences in fracture activity in different orientations and in the connectivity of the fracture cavity in different parts of the reservoir.Then, the development effects of different borehole trajectories are analyzed, and an integrated geological engineering working method is proposed to scientifically guide the design of borehole trajectories and optimization of water injection schemes.An integrated geological engineering approach is proposed to scientifically guide the design of borehole trajectories and optimization of water injection schemes.

| GEOLOGIC BACKGROUND
The Fuman Oilfield is located in the northern depression in the Tarim Basin, which is between the northern uplift and central uplift (Figure 1), and the main oil-producing layer is the limestone reservoir of the Yijianfang formation to Yingshan Formation in the middle Ordovician.Fuman area is controlled by a large strike-slip fault.The reservoir is mainly distributed in strips along the fault zone.The reservoir has huge exploration potential and development benefits.The thickest reservoir is 550 m, and the highest oil production is more than 1600 m 3 /day.
The faults in the northern depression of the Tarim Basin are very developed, widely distributed, with a long evolution history and staged fault activities.Faults have evolved into the current pattern of fault structures through regeneration, inheritance, superposition, and transformation during multiple tectonic movements.
The strike-slip fault has the characteristics of longitudinal stratification, planar zoning, and segmentation along the strike.The movement characteristics of deep and shallow faults are inconsistent, with deep faults mainly characterized by compression and torsion, northeastern strike-slip faults being left-handed, northwestern strike-slip faults being right-handed, and shallow faults being mainly characterized by tension and torsion, with significant differences in movement directions.The strike-slip fault was formed in the mid-Caledonian period, and was reactivated after various tectonic movements were interrupted.9][20] In the same fault zone, the direction of torsion has been changed many times during the tectonic evolution.Its width varies from narrow to wide, and the deformation intensity varies from strong to weak.Tension, compression, compression, and torsion coexist.After karstification, it is funnelshaped and V-shaped on the profile, and the vertical distribution of the reservoir can reach several hundred meters; on the plane, it exhibits distribution characteristics of discontinuous extension, unequal width, and irregular boundaries.
The formation and internal configuration of strike-slip faults are affected by regional tectonic stress.][20][21] During the Himalayan period, influenced by the collision of the Indian and Eurasian plates, the Tarim Basin as a whole was controlled by the horizontal tectonic compressive stress field in the NE-SW direction.As identified from the drilled wells in the Yueman block of the Fuman oil field, the current horizontal maximum main stress direction is approximately NE60°, and the stress direction is basically consistent with the direction of the strike-slip fault (Figure 1B).However, due to the effect of later tectonics, the local stress orientation has been deflected, and the trend of its deflection is consistent with the fracture direction formed by late tectonic movement, which in turn leads to large differences in the degree of fragmentation, fracture The first level tectonic unit division of the Tarim Basin, and (B) the coherent attribute and fault distribution map of the top surface of the third member of the Yingshan Formation in the Fuman Oilfield.The Fuman Oilfield is located between the northern uplift and the northern depression of the Tarim Basin, and is generally controlled by the NE-SW horizontal tectonic compressive stress field.The current maximum horizontal principal stress direction is approximately NE60°, which is basically consistent with the strike-slip fault direction.
activity, and oil and gas enrichment patterns in different fracture zones in the Fuman oil field. 22,23ault-controlled reservoirs are characterized by large scale, irregular shape, and large difference in depth. 24uring the formation of the strike-slip fracture, the horizontal unbalanced tectonic stress makes the fracture zone undergo high shear stress and normal stress, and the formation is deformed and ruptured under the high shear stress, while the broken rock blocks are strongly ground under the high positive stress, both of which together lay the foundation for karst action.
Fracture-controlled reservoirs are generally divided into core and extensional zones.The core zone is mainly developed with large fracture cavities and larger reservoir scales due to strong fracture fragmentation and solution transformation and is the main drilling target; the extensional zone is mainly formed with smaller-scale fracture-cavity reservoirs under the role of associated fracture control.After the formation of the fracturecontrolled reservoir, the fracture surface and the insideout fracture system are controlled by the in situ stress field, which affects the fluid conductivity.In the process of water injection development in the fracture-controlled reservoir, on the one hand, the connectivity between the seam-hole bodies inside the reservoir is governed by the fault-fracture mechanical activity, and on the other hand, the fluid flow inside the fracture cavity is controlled by both the complex medium and the dynamic stress field.

| Quantitative relationship between in situ stress and permeability
The effect of in situ stress on permeability is mainly through the effective stress to change the structural deformation to control permeability.[27][28] (1) For pore-type rocks, the experimental relationship between stress and permeability can be described using the equation 29 where k s is the permeability coefficient under the action of effective stress in the rock, k 0 s is the permeability coefficient under the action of initial effective stress in the rock, σ is the internal stress in the rock, and P is the pore pressure.
(2) Fractured rocks, where fracture deformation is the main cause of permeability change when subjected to forces, can be described mainly according to the power exponential model and cubic model.The power exponential model is mostly used for fracture permeability characterization of carbonate rocks, and the empirical equation for the coefficient is 30 where A is the overwater area, Q 0 is the initial flow rate, P c is the total pressure, P f is the internal pore pressure, and n is a constant.On the basis of the cubic model of the fractured rock experiment, the following relationship is obtained 31 : where R m is the rock classification index, Δε is the strain, φ 0 is the initial porosity, and i = 1, 2, 3.
In general, according to the theoretical model proposed by previous scholars and related experiments, it is confirmed that at low effective stress, the permeability of the rock is high, but as the effective stress increases, the particles become increasingly compact with each other, and the permeability rapidly decreases; when the effective stress reaches a certain level, the above changes slow down significantly. 32

| Fracture-deformation analysis based on physical simulation experiments of large rock samples
According to a similar principle, a physical simulation experiment of high-pressure water injection was carried out by using similar materials to produce large-scale rock samples.Sample size is 281 × 229 × 379 mm, several preexisting fractures were set inside the sample using water-soluble materials.The original stress applied in three directions are σ 1 = 22 MPa, σ 2 = 24 MPa, σ 3 = 7 MPa, indicating a strike-slip-type stress state.Then keep σ 1 , σ 2 unchanged and increase σ 3 to 9, 11, 13, and 15 MPa, with a fluid viscosity of 5 Pa s and an injection rate of 4 mL/min.After the experiment, the extension of fractures on the surface of the sample was observed, and CT scanning was used to reconstruct the threedimensional visualization image of fractures and analyze the distribution characteristics of fractures in the threedimensional space.Figure 2A is a schematic diagram of the experimental scheme.The experimental results (Figure 2B) show that the fracture of the specimen extends along the direction of σ 2 , and with the decrease in the horizontal stress difference, the effect of in situ stress on fracture initiation and extension decreases, and the fracture may extend in the direction of deviation from the horizontal maximum principal stress.
Fractures deviating from the direction of the maximum horizontal principal stress are difficult to communicate, but guided by natural fissures and with a small horizontal stress difference, fractures deviating from the direction of the maximum horizontal stress extend farther.The fractures extend far away in the longitudinal direction, and the fracture surface is smoother and straight, while it extends closer in the horizontal direction.
With the further increase in water injection pressure, at 30°or 45°deviation from the horizontal maximum principal stress, the fractures are communicated in the lateral expansion, and the fracture network is more inclined to be complex.When the horizontal stress difference decreases, it is more helpful for fracture expansion and the formation of a complex fracture network.The orientation with the direction of the horizontal maximum stress at a large angle, in the case of a small horizontal stress difference, once the fractures are generated, the formation of a complex fracture network is greater, but the extension distance is smaller, and the fracture surface is rougher and irregular.
The experimental results support the theoretical analysis and prove that high-pressure water injection can not only activate preexisting fractures and increase the longitudinal communication capacity but also produce new fractures and increase lateral connectivity.

| Mathematical representation equation of fracture and cavity connectivity based on geomechanics
For faults or fractures, the activity related to friction sliding mainly depends on the effective normal stress (σ ne ) and shear stress (τ) on the fault or fracture surface.Each fracture structural plane in the critical sliding state satisfies the following relationship 33 : The ratio of shear stress to normal stress affects the sliding of the fracture surface, which is not only a parameter reflecting the sliding of the fracture structural plane but also an important index reflecting the fracture permeability and fluid.The normal stress and shear stress can be calculated by the relationship between the fracture surface and the in situ stress field: where n i , j are the direction cosine, P p is the pore pressure, MPa, and the stress tensor at a point on the fracture surface for calculating this parameter is defined as where γ is the angle between the normal of the fracture surface and the minimum principal stress (°), λ is the angle between the projection of the fracture direction in the plane and the maximum principal stress formed by the maximum principal stress and the median principal stress (°).On the basis of the above method, the activity, development location, and occurrence information of fractures can be determined by using the relationship between the in situ stress tensor and fracture occurrence on the basis of quantitative prediction of the threedimensional distribution of natural fractures.The ratio of shear stress to normal stress on the fault or fracture surface is the key factor controlling its relative sliding and is also an important geological parameter controlling the permeability of the fracture or fracture zone.It is a positive indicator to reflect the connectivity of the fracture body.The larger the value is, the better the connectivity.
When the fault strike is parallel to or at a small angle to the current maximum horizontal principal stress direction, the shear stress on the fault plane is higher, the normal stress is lower, the ratio of shear stress to normal stress is larger, the shear slip trend is higher, and the activity is better.However, when the fault strike is perpendicular to or at a large angle to the direction of the current maximum horizontal principal stress, the shear stress on the fault surface is lower, the normal stress is higher, and the ratio of shear stress to normal stress is smaller.The fault surface tends to be stable, and the activity is poor. 34hen water is injected at high pressure, some fractures with a high tendency to shear slip are activated.
Since the preexisting fracture surface itself no longer has strength but only frictional resistance, the stress required for reactivation is reduced. 35When high-pressure water injection reaches a certain level, in addition to the preexisting fracture being activated, extensional expansion can occur based on the preexisting fracture, and even new fractures can be created.The shear rupture along the preexisting fracture depends mainly on the strength of the preexisting fracture, and the shear rupture of intact rock depends mainly on the strength of the rock and is related to the angle between the late stress field direction and the preexisting fracture.
In addition, changes in reservoir pressure can also cause changes in fracture activity, which in turn affects fracture-cavity connectivity.For this reason, a critical injection pressure P in is defined, beyond which the activity of the fracture surface can be induced.
in ne (8)   The critical injection pressure indicates the reservoir pressure required when the fault or fracture is active and is an inverse indicator of the activity of the fault or fracture; the smaller the value is, the stronger the activity.
On the basis of the comprehensive consideration of the above two parameters, Zhang et al. 36 proposed a fault or fracture activity index calculation model suitable for high in situ stress, high pore pressure, and complex structures, guided by geomechanical theory and combined with the practical experience of oilfield production.
where G 1 is the normalized value of the ratio of normal stress to shear stress, G 2 is the normalized value of the critical injection pressure, W 1 and W 2 are the weights of the geological properties of the ratio of normal stress to shear stress and critical injection pressure, respectively, and W 2 takes into account the in situ stress field, pore pressure, rock mechanical properties, and geometry of the fracture, which can directly reflect the potential mechanical activity of the fracture zone under the control of the in situ stress field and other factors.It is suitable for quantitative analysis of the connectivity between different fracture bodies, and the larger the value is, the stronger the potential activity of the fracture.The default weights for W 1 and W 2 are generally 50%.WATER INJECTION DEVELOPMENT

| Quantitative optimization technology for wellbore trajectory
The geomechanical properties, such as rock mechanical properties, ground stress field, and fracture parameters, of fault-controlled fracture-cavity reservoirs are controlled by the distribution of faults, which are extremely heterogeneous. 21,37,38On the basis of the accurate tracing and identification of faults, the stress characteristics of the fault surface and the fracture cavity are analyzed, the fracture potential mechanical activity index (FGAI) is used to quantitatively characterize the difference in the mechanical characteristics of the fracture surface, and the FGAI is used to determine the connectivity of the fracture-fault-controlled fracture cavity and divide different connection units.The research shows that the stronger the mechanical activity of the fracture surface, the better the quality of the reservoir and the better the connectivity of the reservoir.The difference in the mechanical properties of the fracture-fault-controlled fracture cavity affects the reservoir connectivity, oil and gas migration, and the effect of water flooding and has a great impact on the wellbore stability.In addition, theory and practice have proven that the horizontal well drilling method for fault-controlled fracture-cavity reservoirs has unique advantages in improving development efficiency. 39n summary, a quantitative optimization method for well trajectories is proposed considering three aspects.First, drilling into high-quality reservoirs should be considered, and fault locations with weak stress concentrations and good activity should be selected.Second, the best effect of water injection in later development should be considered.Laterally, based on the division of the connectivity unit, wells will be deployed in the same connectivity unit, and the length of the horizontal section will be based on the principle that the project can cross multiple fracture surfaces to the maximum extent.Vertically, based on the longitudinal mechanical activity of the fracture, the vertical depth of well drilling and uncovering will be optimized.If the longitudinal connectivity is good (strong activity), wells will be deployed based on the principle of uncovering the top of the reservoir (well A).If the longitudinal connectivity is poor (weak activity), wells with different drilling depths will be deployed to cover the entire reservoir considering the longitudinal distribution of the reservoir (Well B).Third, the fracture strike, regional stress orientation, and wellbore stability are considered, and the well deviation of the horizontal well trajectory is optimized.From the formation mechanism of the strike-slip fracture, it can be seen that the orientation of the maximum principal stress in the region is basically consistent with the strike of the strike-slip fracture.In this state, the orientation with good wellbore stability is in the direction of the minimum principal stress, so drilling along the minimum principal stress orientation can not only ensure the crossing of the fracture surface but also maintain good wellbore stability.In addition, considering that the well trajectory can cross the fault zone to a large extent, on the premise of ensuring the stability of the wellbore, the design of the oblique intersection between the trajectory and the fault trend can increase the crossing length by 40% (Figure 3).

| Gravity displacement technology for fault-control reservoirs
The fracture-cavity reservoir is a triple medium reservoir.Fractures and cavities are easy to deform. 7The permeability is greatly affected by the pressure-sensitive effect.There is a starting pressure gradient in the process of seepage, especially in microfractures and cavities, because the throat is unusually small, the seepage resistance is large, and the pressure drop in the flow process is more prominent.The sharp reduction in formation pressure makes the formation deformation and the pressure sensitivity damage more serious.In the early stage of the development of fault-control reservoirs, the formation energy is high, and the oil well blowout is high, but the production decreases rapidly due to the rapid pressure drop.In view of this problem, highpressure water injection countermeasures are proposed, and the method of reciprocating circulating water injection is adopted to improve oil recovery.A previous paper confirmed through theoretical analysis and experimental simulation that the fracture-cavity body will deform due to pressurization during high-pressure water injection, and the local stress field will also change, resulting in a shear slip on the fracture surface and even new cracks. 40This increases the vertical and horizontal communication ability.At this time, the well was shut in and soaked.Due to the gravity differentiation of oil and water, obvious oil and water displacement will occur after a certain period of time, and the oil and gas will be uplifted under high pressure.When the well is opened for pressure relief and oil production, flowing oil production can be realized.The local formation pressure drops again to reduce production, and the above methods can continue to be used to improve oil and gas recovery.
Taking the Fuyuan-210 fault zone in the Fuman Oilfield as an example, 11 oil wells are currently in production in this fault zone.Static analysis focused on the geomechanical activity of the fault zone to determine the connectivity of the faults and the design of interfering test well plans based on the static classification results.Finally, in combination with the production performance characteristics, the Fuyuan-210 fault zone is divided into four connected units from northern to southern on the plane (Figure 4).
The wells in the Fuyuan-210 fracture zone rely on natural energy to produce, and it is difficult to stabilize production.On average, the production capacity of a single well dropped from 1246 t/day at the beginning to 304 t/day after 404 day of production, and five wells had stopped spudding before the implementation of unit water injection.The remaining six wells were close to stopping spudding, and the average single-well recovery rate was only 6%.
Therefore, a water injection test was carried out, taking the FY1-H3 well as an example, as shown in Figure 5.The deformation of the fault and fracture cavity F I G U R E 3 On the basis of fault characterization, a three-dimensional geomechanical model is established to determine the distribution of the in situ stress field and fault activity distribution (A), and the well trajectory is designed accordingly.The length of the horizontal section of the well trajectory is based on the principle that it can cross multiple fault surfaces to the greatest extent.In the vertical direction, the vertical depth of drilling and excavation is optimized based on the longitudinal mechanical activity of the fault.If the vertical activity is good, the well (well A) is arranged based on the principle of uncovering the top of the reservoir.If the vertical activity is poor, the vertical distribution of the reservoir is considered, wells (well B) with different drilling and excavation depths are deployed, and the well trajectory needs to consider the stability of the wellbore; as shown in Figure (B), the direction with good wellbore stability is located in the direction of the minimum principal stress.Therefore, drilling along the direction of the minimum principal stress can not only ensure crossing the fracture surface but also maintain good wellbore stability.
F I G U R E 4 According to the activity of the fault, the Fuyuan-210 fault can be divided into four connected units on a plane, with FY210-H7 in the north being an isolated unit.The geological and mechanical activity of the fault around the well is very poor; the central FY210H, FY210-H1, FY210-H3, FY210-H4, and FY210-H6 are the same connected units; FY210-H10 and FY210-H12 are the same connected unit; and the southern FY210-H14 is an isolated unit.
under high-pressure water injection conditions is simulated.First, by injecting water into the first set of reservoirs, the pressure of the reservoir gradually increases from the original 91.7 MPa.When the pressure reaches 101 MPa, the fractures between the first set and the second set of reservoirs are activated and connected.When the pressure increases to 106 MPa, the two sets of reservoirs are fully connected, and the internal pressure of the reservoir is adjusted to 93.4 MPa.If high-pressure water injection is continued, when the pressure of the reservoir reaches 117 MPa, the fractures between the second and third sets of reservoirs are activated and connected, and the internal pressure of the reservoir is adjusted to 95.2 MPa.In addition, it is found that the displacement effect will decrease to a certain extent after multiple rounds of water injection, which may be due to the short duration of high-pressure water injection and the short opening time of the fracture channel, and the injected water cannot effectively enter the fracture channel.Therefore, it is necessary to ensure the water injection time and soak the well for a certain time after the water injection to maintain the high pressure at the bottom of the well and then open the well for pressure relief after the oil and water are fully replaced.The practice shows that the oil production of the FY1-H3 well is more than 9500 t, and the replacement rate is 0.31 after multiple rounds of water injection.The expected effect is achieved.
Connected unit 2 of the Fuyuan-210 fault zone was selected as the unit injection for implementation and effect analysis (Figure 6).In this unit, the FY210-H1 and FY210-H4 wells were drilled and uncovered 81.5 and 85.0 m of reservoir, respectively, due to the stoppage of water injection, which was a shallow injection in the unit.After only 15 day of water injection, the FY210-H3 well was effective, and the oil pressure increased steadily, while the FY210H well in the shallow part of the reservoir did not respond significantly.This proves that water injection in the fault-controlled reservoir is mainly influenced by gravity, with water flowing to the lower part of the reservoir first and the deeper wells receiving the effect first.At present, the cumulative water injection in this unit is 7.4 × 10 4 m 3 , and the cumulative oil increase in the affected wells is 2.6 × 10 4 t.
Connected unit 3 of the Fuyuan-210 fault zone was selected as the high-pressure water injection for implementation and effect analysis.As shown in Figure 7, the poor connectivity around the well as judged from the production data is consistent with the connectivity predicted above based on fracture activity.The injection pressure equivalent density required to activate the fractures around the well is predicted to be 1.40-1.50g/ cm 3 .The maximum daily oil production after the well is put into production is 182 t/day, and the average daily oil production is 45 t/day.After stopping the injection, water injection is implemented to drive the oil, the design injection pressure is approximately 20 MPa, and the density of the injected water is 1.16 g/cm 3 .The density is about 1.45 g/cm 3 , which is the condition for activating the fracture around the well.After the implementation of water injection, the wellhead pressure rose to a maximum of 37 MPa after 58 days of well stalling and returned to the level of the early test production, equivalent to a daily oil production of 201 t.The well accumulated 2.36 × 10 4 m 3 of water injection and increased oil by 0.67 × 104 t, with a significant oil replacement effect.F I G U R E 7 The fault position encountered during FY210-H7 well drilling has poor activity, and it is predicted that the injection pressure required to activate the faults around the well is 1.40-1.50g/cm 3 .To achieve the conditions for activating the fault around the well, the design injection pressure equivalent density is approximately 1.45 g/cm 3 .After implementing pressurized water injection for 58 days, the well pressure rose to the highest level of 37 MPa, returning to the initial level of trial production.
The above fault-control carbonate water injection technology has been fully implemented in the Fuman Oilfield.Compared with similar oilfields without this technology, the indicators of the northern depression oilfield are significantly higher than those of similar oilfields without this technology in terms of the average cumulative production of a single well, the average production cycle of a single well, the degree of reserve utilization and the replacement rate of water injection and oil recovery in the past 3 years.The first three indicators are increased by 124% and 34%, respectively, 54%, and the replacement ratio of water injection and oil production decreased by 57%.

| CONCLUSIONS
(1) Large-scale fractures and high-angle fracture systems in the deformation of strike-slip faults are the key factors affecting reservoir quality.On the one hand, high-pressure water injection can activate preexisting fractures, and on the other hand, it can extend on the basis of preexisting fractures.The expansion can even generate new fractures, which promote the interconnection of the fault-controlled fracture-cave bodies in the vertical and horizontal directions.(2) During the process of high-pressure water injection, the coupling change between mechanics and flow occurs inside the fracture body, the seepage environment is improved, and the oil and gas recovery factor is improved through cyclic lifting.
(3) According to the shape and occurrence of the fault body and the dynamic shear deformation connectivity of the fault surface, the best well point and well trajectory of the directional well can be optimized, and the water injection scheme can be optimized.(4) In the Fuman Oilfield Test Area in the Tarim Basin, the single-well production increased by 1.45 × 10 4 t through high-pressure water injection, the cumulative oil increase of the same fracture-cavity body increased by 4.63 × 10 4 t.(5) The integrated working method of geomechanics modeling and geological engineering not only fits the geological characteristics of ultradeep faultcontrolled carbonate reservoirs but also effectively guides the relevant technical support in water injection development, which not only directly creates huge economic benefits but also has important reference significance for the efficient exploration and development of the same type of complex oil and gas reservoirs and plays a leading and exemplary role.

F
I G U R E 2 Similar materials are used to produce large-scale rock samples for high-pressure water injection physical simulation experiments.(A) The experimental scheme and sample photos, with several preexisting fracture surfaces built-in, σ 1 , σ 2 , and σ 3 are the three principal stresses.(B) For the experimental results, the fractures first extend further in the longitudinal direction, and as the pressure increases, the fractures expand laterally.

F
I G U R E 5 (A) Distribution characteristics of in-situ stress in fault zones.(B) Dynamic changes in stress field during high-pressure water injection process.The pressure of the reservoir gradually increases from the original 91.7 MPa.(C) When it reaches 101 MPa, the fractures between the first and second sets of reservoirs are activated and begin to connect.(D) When the pressure increases to 106 MPa, the two sets of reservoirs are fully connected, and the internal pressure of the reservoir is adjusted to 93.4 MPa; (E) continuing to maintain highpressure water injection, when the pressure of the reservoir reaches 117 MPa, the fractures between the second and third sets of reservoirs are activated and connected, and the internal pressure of the reservoir is adjusted to 95.2 MPa.

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I G U R E 6 (A) Schematic diagram of the development of the fracture-cave body and the location of the water injection well (FY210-H1 and FY210-H4).(B) shows the fault activity around the water injection well.The fault location encountered during the drilling of the FY210-H3 well shows good activity, while the FY210 well shows poor activity.After 15 days of water injection, the oil pressure of the FY210-H3 well steadily increased, indicating that the well achieved the effect of water injection, while the oil pressure of the FY210H well did not significantly increase.The practical effect is consistent with the simulation results.