Impact of Fracture Closure on Productivity Decline of Unconventional Wells

Abstract

With the rapid pace of drilling wells to tap unconventional oil and gas resources in the U. S., there is a need for further understanding of the fundamentals of reservoir mechanics that control well productivities. Wells with more than 5 years of data provide the opportunity to understand flow mechanisms affecting well productivity. What is particularly important is to test the validity and appropriateness of decline curve forecasting methods advocated in the literature over the last several years. To explain the unique and similar performance trends from unconventional wells, there are a number of issues that are gradually getting attention. Among these are the causes of rapid production decline seen after the initial peak. Certainly the physics of flow conditions causing the decline is not captured when regression analysis of production data is used with various decline models. Based on earlier studies, there is selfsimilarity among fractures formed during hydraulic fracturing. As discussed in the literature; the transient pressure behavior of complex self-similar fractures is equivalent to that for a single fracture. As such it is the flow capacity of the equivalent fracture that controls the behavior seen in actual performance of hydraulically fractured wells.To test the applicability and weaknesses of commonly practiced regression models, we examined the performance of number of wells with production histories exceeding five years We used more than 40 examples from various shale plays all showing the loss of fracture quality resulting in lower flow capacity within the fracture network. The dynamic change in flow capacity is certainly not captured when decline curves are used that do not honor the flow regime's changes. As such, there can be major uncertainties associated with estimated EUR's from decline analysis techniques

A semi‐analytical model for capturing dynamic behavior of hydraulic fractures during flowback period in tight oil reservoir

“…During the flowback period, there are many researches 6,7 found that the parameters of the fracture calculated by two‐phase flow data after hydrocarbon breakthrough are less than that calculated by single‐phase flow data before hydrocarbon breakthrough. In addition, the permeability loss of fracture during the production was also observed by well‐testing analysis 14 and production decline analysis 15 of field data. These evidences show that the closure of the fracture, causing the fracture properties (eg, fracture permeability) deteriorate significantly, occurs with the reduction of fluid pressure within the fracture throughout the flowback and production.…”