Evaluation of Haynesville Shale Vertical Well Completions With a Mineralogy Based Approach to Reservoir Geomechanics

Abstract

Abstract This paper presents a methodology for characterizing the mineralogy and geomechanical properties of the Haynesville Shale. The results from two case study wells demonstrate how a perforating strategy based on mineralogy and geomechanical properties derived in part from mineralogy can improve hydraulic fracture stimulation performance. A full suite of openhole logs (acoustic, NMR, density-neutron, and mineralogy) provides the means for estimating both geomechanical properties and reservoir quality. An accurate measurement of total organic carbon with minimum core calibration is obtained from new wireline pulsed-neutron logging technology. Utilizing primarily openhole logging data, a micromechanical model simulates axial and radial deformations of a core sample under triaxial stress. It provides the static rock mechanical properties and strengths at different confining conditions for every depth interval. A new input to the micromechanical model is the mineralogy characterization derived from a wireline pulsed neutron tool. The static rock mechanical properties and TOC derived from these methods provide the key to understanding the fracturing potential of a zone in the Haynesville Shale. Two log examples show how optimized perforation placement based on these approaches can positively impact production. Tracer logs indicating vertical fracture containment and production data provide a validation of the approach. A post-mortem analysis of these well completions suggests that using the results of these models for fracture and completion design results in better production than wells completed differently in similar formations. The described approach brings together mineralogy, TOC, and mechanical rock properties for a complete evaluation of Haynesville Shale reservoirs with a view toward optimizing completion costs. Introduction The inherent risk associated with resource plays such as shale gas plays is mitigated by a high well success rate and high initial production. A shale gas well that does not produce at economical rates, therefore, is a major setback for operators. Both geological and well logging data are utilized to determine which zones are most likely to fracture and which are the most productive (Jacobi et al., 2008). The petrophysical, mechanical, and mineral characteristics of the play can vary significantly (Economides et al., 2008). The Haynesville Shale is one such play where careful planning and execution can be the difference between a productive economic well and a poorly completed well. Vertical wells are drilled in the Haynesville Shale to initially evaluate the play, test completions, and plan hydraulic fracturing strategies. The choice of perforation depth intervals is often based on limited geological knowledge because it is a relatively new field and there is uncertainty about the lithologies comprising the strata. A lack of knowledge about the complexity of the formation across the basin contributes to this uncertainty. Conventional log responses are at times difficult to interpret. There are effects due to relatively high clay content and organic matter in the rock matrix not usually present in other conventional reservoirs where conventional responses are less challenged. These effects make gas-rich sweet spots difficult to identify unless new technologies are incorporated for reference. The goal of formation evaluation in gas shales is to identify preferable zones for gas productivity from both a petrophysical and engineering standpoint.