Shear Dilation Diagnostics: A New Approach for Evaluating Tight Gas Stimulation Treatments

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractMany tight gas reservoirs require fracture stimulation to achieve commercial outcomes. These reservoirs can often be characterized geologically and geomechanically by high deviatoric stresses and hard, naturally fractured rock. Stimulation treatments in such reservoirs may create complex fracture networks from a combination of shear and tensile failures. Water fracs can be used where shear failure is anticipated to dominate. However, in these environments few practical modeling tools exist to determine [1] the level of permeability enhancement, [2] the degree of permeability retainment during drawdown and [3] the Stimulated Rock Volume (SRV). This paper seeks to provide the engineer with a suite of tools capable of achieving these goals. This paper presents a dual porosity, pressure dependent permeability reservoir simulation model that was devised to honor shear failure mechanisms [also called shear dilation] using basic geological characterization. The assumptions of this model and the pragmatic selection of first order effects are discussed. Using the results of this simulation model, three families of diagnostic tools are presented.The first category is that of Treatment Diagnostics (TD) which include bottomhole pressure evaluation, injectivity and fall-off analysis. The second approach is called Seismic Based Reservoir Characterization (SBRC), which uses the microseismic to determine the SRV as well as provide estimates of the initial and stimulated fracture network properties. The third category is Post Treatment Diagnostics (PTD), which incorporates the evaluation of pressure drawdown characteristics.Finally, this paper compares these individual approaches and provides a workflow to evaluate data on future wells.

Mechanisms of Casing Deformation during Hydraulic Fracturing in the Horizontal Wells of the Weirong Shale Field

“…During hydraulic fracturing, Chipperfield et al proposed that the initiation and propagation of fractures formed tensile fractures and caused shear deformation. 17 Fluid injection-induced aseismic slip of faults and surface ruptures were proposed by Wei et al 18 Based on the analysis of microseism data, Qian et al observed that the casing deformations in the Sichuan basin occurred primarily due to shear slips in the large-scale natural fracture areas. 19 Bao and Eaton suggested that different mechanisms could trigger fault activation during and after hydraulic fracturing.…”

“…As a result, recently, several researchers have explored the shear deformation caused by fault slides during hydraulic fracturing. During hydraulic fracturing, Chipperfield et al proposed that the initiation and propagation of fractures formed tensile fractures and caused shear deformation . Fluid injection-induced aseismic slip of faults and surface ruptures were proposed by Wei et al Based on the analysis of microseism data, Qian et al observed that the casing deformations in the Sichuan basin occurred primarily due to shear slips in the large-scale natural fracture areas .…”