Investigation on Interference Test for Wells Connected by a Large Fracture

Abstract

Pressure communication between adjacent wells is frequently encountered in multi-stage hydraulic fractured shale gas reservoirs. An interference test is one of the most popular methods for testing the connectivity of a reservoir. Currently, there is no practical analysis model of an interference test for wells connected by large fractures. A one-dimensional equation of flow in porous media is established, and an analytical solution under the constant production rate is obtained using a similarity transformation. Based on this solution, the extremum equation of the interference test for wells connected by a large fracture is derived. The type-curve of pressure and the pressure derivative of an interference test of wells connected by a large fracture are plotted, and verified against interference test data. The extremum equation of wells connected by a large fracture differs from that for homogeneous reservoirs by a factor 2. Considering the difference of the flowing distance, it can be concluded that the pressure conductivity coefficient computed by the extremum equation of homogeneous reservoirs is accurate in the order of magnitude. On the double logarithmic type-curve, as time increases, the curves of pressure and the pressure derivative tend to be parallel straight lines with a slope of 0.5. When the crossflow of the reservoir matrix to the large fracture cannot be ignored, the slope of the parallel straight lines is 0.25. They are different from the type-curves of homogeneous and double porosity reservoirs. Therefore, the pressure derivative curve is proposed to diagnose the connection form of wells.

Interpretation of pressure interference tests for wells connected by a large hydraulic fracture

“…1424.52q sc T Han et al (2019) also defined dimensionless fracture length as: Since the fracture connects the two wells, the fracture length can be taken as the distance between the wells.…”

“…The other model, with a crossflow from the matrix to large fracture, was also proposed by Han et al (2019) in the Laplacian domain to be Laplacian pressure derivative is estimated by the Laplace properties and is determined by: Han et al (2019) also defined the diffusivity ratio, C f , and permeability ratio, F D , as follows:…”

“…They, however, did not provide equations to estimate fracture conductivity, fracture permeability, or any other parameter. Han et al (2019) presented two analytical solutions to study the pressure behavior between two wells connected by a large fracture. One model considered the crossflow between the matrix and fracture, whereas the other one did not, but they did not provide a direct analytical interpretation technique.…”

“…One model considered the crossflow between the matrix and fracture, whereas the other one did not, but they did not provide a direct analytical interpretation technique. Therefore, the current study is based on the two models proposed by Han et al (2019) to provide two interpretation techniques: (1) conventional analysis and (2) Tiab's direct synthesis (TDS) technique, Tiab (1993), which were tested with simulated examples. On the one hand, as it is well-known, the straight-line conventional analysis method uses a plot of pressure against a given function of time from which the slope reservoir parameters can be estimated.…”

“…Some applications of the TDS technique in interference testing were presented by Escobar et al (2008Escobar et al ( , 2018Escobar et al ( , 2020 for radial systems, linear and spherical systems, and naturally fractured reservoirs in radial systems, respectively. For further information on the TDS technique, refer to the works by Escobar (2015Escobar ( , 2018a and Escobar et al (2018a), Han et al (2019) introduced two models to be used with shale formations to account for the interference of two multistage hydraulically fractured wells that communicate by a large fracture. One model includes the crossflow from the reservoir matrix to the fracture, while the other one, referred to as the simple model here, does not.…”