Flow Response of Propped Fracture to Repeated Production Cycles

Abstract

ABSTRACT Once a reservoir is hydraulically fractured, the fracture may experience several repeated production/shut-in cycles. Evidence of reduced rate of recovery as wells are placed back on production, has been noted in gas wells that have been exposed to this type of cycling. As the cycling process is repeated, the propped fracture undergoes the ups and downs of closure stress, resulting in a gradual reduction in fracture conductivity. To observe the phenomenon, a propped fracture using formation rock, was subjected to cyclic loading in the laboratory. Change in fracture conductivity with time and the number of cycles was measured. Interaction between proppant and formation rock was examined. One sand size and two synthetic proppant sizes were evaluated. Two formation rock types of different hardnesses were used in simulating the fracture. At the same closure stress level, fracture conductivity continuously decreased as the loading cycle is repeated. The amount of reduction in conductivity depended upon the rock hardness and proppant size. For the same hardness rock, the magnitude of closure stress dictated the suitable proppant size to minimize the cyclic effect. Thus, the combination of information obtained through this study is a tool to select a proppant to minimize the cyclic effect. Suggestions and optimum design criteria to circumvent or minimize the repeated shut-in effect are presented along with the test results.