Estimation of the Half-Length of Non-Simultaneous-Closed Fracture Through Pressure Transient Analysis: Model and Case Study

During water-flooding development, severe water breakthrough has been observed in fractured wells. It is essential that determine the reason for water-breakthrough to improve the performance of production wells. However, the conventional pressure-transient analysis model hardly characterizes fracture-induced pressure response and fracture half-length, leading to erroneous results. This paper aimed at present an approach to estimate the half-length of non-simultaneous fracture induced in a relatively economical way. The non-simultaneous fracture closure flow (NFCF) model was proposed to characterize flow in induced fracture. To better characterize pressure response in induced fracture, we first modeled fluid flow in fracture with variable conductivity by two-part, variable-conductivity-linear flow and low-conductivity-linear flow. At the same time, fracture closure was considered to occur twice according to the pressure response of water injection wells, and its condiction followed experimental results. As a result, a semi-analytical solution was developed. We compared it with the finite-conductivity model to certify the accuracy. A new flow regime (the non-simultaneous fracture close linear flow) was discovered and behaved as two peaks on the pressure derivative curve. It will shorten the half-length of induced fracture if the new flow regime is ignored. Case studies showed that the NFCF model matched well with field data, which validated the practicability of the proposed approach. Our results might help accurately understand the reason for the water breakthrough - enormous the half-length of induced fracture was ignored in the past. In addition, the results also have provided significant insight for the operators could make reasonable decisions, reasonable well spacing and water-flooding rate, to improve production and water injection wells performance.