Diagnostic Fracture Injection Testing Tactics in Unconventional Reservoirs

Abstract

Abstract To achieve optimal production from unconventional reservoirs, it is useful to determine the permeability, pore pressure, and state of stress of rock strata. Doing so will lead to properly designed treatments, realistic predictions of well performance, and a basis for normalizing reservoir contribution when evaluating completion and stimulation effectiveness. An effective way to derive the necessary reservoir information is to conduct in-situ pressure transient tests. Since it is difficult to inject fluid into or withdraw fluid from the pore network of tight rock, diagnostic fracture injection tests (DFIT) have been employed to create an analyzable pressure decline response, as well as to derive the minimum horizontal stress via fracture closure identification. This paper is a study of numerous DFITs conducted in unconventional reservoirs throughout the world to evaluate the reservoir and geomechanical characteristics of the pay zone and bounding intervals. Within this body of work, experiments were implemented to study the impact of testing methods on the test response and various types of analysis methods documented in the literature were implemented and compared. The paper summarizes findings and introduces tactics for planning/conducting tests and evaluating results in a variety of unconventional reservoir types. Topics covered in the paper include: Defining test objectives Test planning and strategies ○ Tactics for selecting injection rates and volumes ○ Downhole shut-in techniques for hastening fracture closure and radial flow regime development. ○ Vertical vs. horizontal wells ○ Multiple injection-falloff cycles. ○ Multi-interval tests ○ Multiple non-communicating pressure gauges. ○ Tactics for understanding test height Pre-test fracture modeling for selecting injection volumes and rates and test intervals. Procedure/execution Reservoir and geomechanical considerations ○ Sub-pressured reservoirs ○ Fracture closure ○ Impact of natural fractures ○ Near-wellbore fracture complexity