Methodology for Evaluation and Design Improvement of Multifractured Horizontal Wells in Tight Gas Reservoirs Using Pressure-Normalized-Rate-Transient Diagnostics

摘要

An approach is presented that provides a stage-by-stage evaluation of the performance efficiency of a multi-fractured horizontal in tight reservoirs (actually any type of reservoir), by using results from PLT measurements in combination with specialized pressure-normalized rate-transient diagnostics, that treats well production history as an extended drawdown. The methodology is unique, and allows for; 1) evaluation of the performance efficiency of each individual fracture in terms of the effective properties from each individual fracture stage, namely fracture length (Xf,effective), conductivity (kfbf)effective and dimensionless conductivity (CfD). To the best of our knowledge, the results are the only direct measurement available of the performance of hydraulic fractures in a multi-fractured horizontal, unless the decision is made to isolate and do build-up test for of each individual fracture stage. An expensive and time consuming proposition. The results are superior to PTA results and are action oriented, since 1) the well does not require to be shut in, 2) the well can be in transient flow and this data is used in the interpretation of the fracture and reservoir characteristics, and 3) the optimization and design improvement follow from these evaluations. Optimization is done in terms of improvement of deliverability and of the underperforming fracture parameters such as: poor conductivity (and how to improve it), under- designed fractures (Xf,effective < Xf,design), bypassed zones, zones without a frac, zones to be plugged back, or non-contributing zones. To complement the methodology we use the dimensionless productivity index (JD) to evaluate the performance efficiency and the Stimulation Index (SD) to evaluate the degree and effectiveness of stimulation of a multi-fractured horizontal.