A Semianalytical Methodology To Diagnose the Locations of Underperforming Hydraulic Fractures Through Pressure-Transient Analysis in Tight Gas Reservoir

Abstract

Summary The increasing activities in tight reservoir exploitation through fractured wells have attracted interests of pressure-transient analysis (PTA) for well-performance evaluation. The production rates of different fractures were assumed to be equal in previous models. However, different fractures have unequal contributions to the total-gas-production rate because of the differences of fracture scale (e.g., half-length, height), heterogeneity of gas saturation, formation damage, and fracture closure. This paper considers the effect of unequal gas-production rate of each fracture (UGPREF) on pressure-transient behaviors, and develops a semianalytical methodology to diagnose the specific locations of underperforming fractures through PTA by use of bottomhole-pressure (BHP) data. First, new semianalytical solutions of a multifractured horizontal well (MFHW) in a tight gas reservoir are derived on the basis of the Green function (Gringarten and Ramey 1973) and Newman product method (Newman 1936). Second, the model is validated by comparison with the numerical model in KAPPA Ecrin (Saphir) software (Essca 2011). Third, type curves are developed, and sensitivity analysis is further investigated. Results show that there exist clear distinctions among these type curves between equal gas-production rate of each fracture (EGPREF) and UGPREF. The early radial flow is distinguishable and behaves as a horizontal line with the value of 0.5/N* (N* = N for EGPREF, N*≠N for UGPREF) in the pseudopressure-derivative curves when the interferences between fractures do not overlap this period. If the early-radial flow was mistakenly regarded as pseudoradial flow, the interpreted permeability would be N* times smaller than the accurate result. Furthermore, the methodology is applied to a field case of the Daniudi tight gas reservoir in the Ordos Basin, which illustrates its physical consistency and practicability to diagnose the specific locations of underperforming hydraulic fractures through pressure-history matching. It also provides feasible references for reservoir engineers in well-performance evaluation and field strategy (e.g., refracturing, acidizing, or other stimulation treatments) to enhance hydrocarbon production.