The Hydraulic Fracturing Optimization for Stacked Tight Gas Reservoirs Using Multilayers and Multiwells Fracturing Strategies

Based on a geology-engineering sweet spot evaluation,the high-quality reservoir zones and horizontal well landing points were determined.Subsequently,fracture propagation and production were simulated with a multilayer fracturing scenario.The optimal hydraulic fracturing strategy for themultilayer fracturing networkwas determined by introducing a vertical asymmetry factor.This strategy aimed to minimize stress shadowing effects in the vertical direction while maximizing the stimulated reservoir volume(SRV).The study found that the small vertical layer spacing of high-quality reservoirs and the presence of stress-masking layers(with a stress difference of approximately 3∼8 MPa)indicate that interlayer stress interference from multilayers and multiwells fracturing between neighboring developed formations could affect the longitudinal propagation of the reservoirs.In addition,this study investigated well spacing optimization by comparing uniformly spaced wells(100–300 m)with asymmetric spaced wells(200 m upper layer,250 m lower layer).Numerical results indicated that asymmetric spaced well placement yielded the largest stimulated reservoir volume(SRV)of 73,082 m^(3),representing a 65.42%increase compared to 100 m spaced wells.Furthermore,four different hydraulic fracturing sequences(interlayer,up-down,down-up,and center-edge)were compared for multilayer and multiwell networks.The center-edge sequence exhibited the lowest vertical asymmetry factor(0.71)and the least stress shadowing effects compared to the other sequences(0.78 for interlayer,0.75 for up-down,and 0.76 for down-up).This sequence also achieved the largest SRV(486,194m^(3)),representing an 11.87%increase compared to the down-up sequence.Therefore,the center-edge fracturing sequence is recommended formultilayer development in this block.These results offer valuable insights for optimizing well placement and fracturing sequence design in multilayer well networks,ultimately advancing the development of multilayer fracturing technology in the region.

Pressure Buildup Analysis for a Well in a Closed, Bounded Multiwell Reservoir

A general method has been developed for analyzing pressure buildup data from a well located in a system with both production and injection wells in a closed, bounded two-phase flow reservoir. The proposed method enables one to calculate the total mobility or permeability-thickness product, the skin factor, the average drainage-area pressure and the injection-production ratio （at the instant of shut-in） with accuracy from pressure buildup （or falloff） data dominated by a linear trend of reservoir pressure. Out of thousands of well tests, several typical field examples have been presented to illustrate the application of the proposed method for analyzing pressure transient data from a well located in a water-injection multiwell reservoir. And the possible application of this method to heterogeneous systems such as naturally fractured reservoirs is also discussed. Approaches to aid practicing engineers in verifying the buildup interpretation （or recognizing the interference of offset wells） are presented. Extension of the presented method to a gas well located in a multiwell gas reservoir is also suggested

ANALYSIS OF TWO-PHASE FLOW PRESSURE BUILDUP DATA FROM A WELL IN ANINFINITE MULTI WELL RESERVOIR

A general method has been developed for analyzing two-phase flow pressure buildup data from a well located in a system of both production and injection wells completed in an infinite muhiwell reservoir. The analysis technique assumes that the tested well has established its own drainage area before shut-in and a linear reservoir pressure trend dominates the well pressure behavior at the instant of shut-in. And for the two-phase flow problems the horizontal saturation gradients are assumed to be negligible. The entire pressure rcsponse, whether or not conventional semilog straight lines exist, can be analyzed and the Injection-Production Ratio （IPR）, the total fluid （oil/water） mobility, the average drainage-area pressure, and also the skin factor can be calculated much easily. The validity and applicability of the method are demonstrated by a field example. The technique by using the type curves for analyzing the pressure-buildup data is also presented here.

Simplification workflow for hydraulically fractured reservoirs

Production from unconventional formations,such as shales,has significantly increased in recent years by stimulating large portions of a reservoir through the application of horizontal drilling and hydraulic fracturing.Although oil shales are heavily dependent on oil prices,production forecasts remain positive in the North-American region.Due to the complexity of hydraulically fractured tight formations,reservoir numerical simulation has become the standard tool to assess and predict production performance from these unconventional resources.Many of these unconventional fields are immense,consisting of multistage and multiwell projects,which results in impractical simulation run times.Hence,simplification of large-scale simulation models is now common both in the industry and academia.Typical simplified models such as the“single fracture”approach do not often capture the physics of large-scale projects which results in inaccurate results.In this paper we present a simple,yet rigorous workflow that generates simplified representative models in order to achieve low simulation run times while capturing physical phenomena which is fundamental for accurate calculations.The proposed workflow is based on consideration of representative portions of a large-scale model followed by postprocess scaling to obtain desired full model results.The simplified models that result from the application of the proposed workflow for a single well and a multiwell case are compared to full-scale models and the“single fracture”model.Comparison of fluid rates and cumulative production show that accurate results are possible for simplified models if all important components for a particular case are taken into account.Finally,application of the workflow is shown for a heterogeneous field case where prediction studies can be carried out.