Diagnostic Fracture Injection Test Analysis Method Addresses Layered Rocks
Authors: Carpenter Chris 
Published: January 2021

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 199690, “Diagnostic Fracture Injection Test Analysis and Interpretation in Layered Rocks,” by Shuang Zheng, SPE, Ripudaman Manchanda, SPE, and HanYi Wang, The University of Texas at Austin, et al., prepared for the 2020 SPE Hydraulic Fracturing Technology Conference and Exhibition, The Woodlands, Texas, 4-6 February. The paper has not been peer reviewed.

Formation-property estimations based on diagnostic fracture injection tests (DFITs) typically are based on analysis of pressure data assuming the closure of simple planar fractures in homogeneous reservoirs. These interpretations are incorrect when dealing with complex reservoir environments such as layered reservoirs with different properties and stresses. The complete paper investigates the effect of such complex environments on DFIT interpretation and presents a systematic method to analyze the data.

Model Description

A fully integrated hydraulic fracturing and reservoir simulator is used in this paper to simulate a DFIT. This simulator has been developed for designing and evaluating pad-scale fracturing treatments. It was then extended from a single-phase flow model to a multiphase black-oil-flow model and from a single-well fracturing simulator to an integrated fracturing and reservoir simulator. An energy-balance model was incorporated into the simulator to consider temperature changes. The fully implicit geomechanical hydraulic fracturing simulator was also extended to an integrated equation-of-state-based compositional fracturing and reservoir simulator in recent work.

This simulator, which has been used in the literature and is discussed in detail in the complete paper, couples the reservoir fracture/wellbore system and has the capability to simulate the life cycle of wells: hydraulic fracturing, shut-in, flowback, primary production, and improved oil recovery.

Base Case

In the base case, a small amount of fluid is injected into the wellbore and the well is shut in for 10 days to mimic a DFIT job. The simulation domain is 400×400 m2 in the horizontal plane and 200 m in the height direction. The perforation clusters are placed in the middle of the domain. The bottomhole pressure vs. time is computed and plotted in this simulation. The simulation involves propagation of a single vertical fracture from a horizontal wellbore drilled in a formation with layered stress heterogeneity.

The fracture maintains the largest width in the middle low-stress region, and the two low-stress regions below and above the middle low-stress region also have a large width compared with the fracture-tip regions and the high-stress regions. During fracture closure, fracture width decreases; however, the fracture width in the low-stress region is always higher than in the high-stress region.

Results and Discussion

The authors applied the numerical DFIT model to study the effect of different layer properties on DFIT signature and its interpretation. The simulation results indicate that most of the layer proper-ties have a major effect on DFIT signature and interpretation.