Proper Evaluation of Shale-Gas Reservoirs Leads to More-Effective Hydraulic-Fracture Stimulation

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 123586, "Proper Evaluation of Shale-Gas Reservoirs Leads to a More Effective Hydraulic-Fracture Stimulation," by Donald Kundert, SPE, and Mike Mullen, SPE, Halliburton, originally prepared for the 2009 SPE Rocky Mountain Petroleum Technology Conference, Denver, 14–16 April. The paper has not been peer reviewed. Shale-gas formations currently are being explored in the Rocky Mountain region. Whether the well is drilled vertically or horizontally, shale-gas wells need hydraulical fracture stimulation to produce commercial amounts of natural gas. Because each shale play has unique attributes, a systematic approach to well construction, data collection, and prefracture diagnostics is an essential component in the quest for the most effective hydraulic-fracture stimulation and the best chance to achieve commercial gas production. Introduction In recent years, natural-gas production from shale has become of increasing interest in the quest for future energy supplies. During the last 40 years, the petroleum industry has progressed from conventional gas reservoirs, to tight gas reservoirs, to ultralow matrix-permeability unconventional shale-gas reservoirs. Each type of reservoir has presented its own unique challenges. The matrix permeability of the reservoir of interest has gone from millidarcies (conventional), to microdarcies (tight gas), to nanodarcies (shale). It then becomes essential for the prospective shale-gas reservoir to have enhanced permeability beyond the matrix permeability, usually in the form of existing natural fractures. Even with enhanced permeability from natural fractures, a well-designed hydraulic-fracturing program is needed to provide successful production results. A wide variety of mineralogy exists among formations that are classified as shales. Shale is not a rock type and is described by the formation-grain size and fissility of the rock. In the initial phases of a new shale play, considerable attention is required to describe the shale accurately. This can be achieved through laboratory testing of shale-formation samples, extensive openhole electric logging, physical pump-in testing, and other methods. Shale-Gas-Evaluation and -Stimulation Process The full-length paper proposes a step-by-step procedure for planning, evaluating, and stimulating potential shale-gas reservoirs in a systematic process. The intent is to gain a thorough understanding of the resource so that commercial production can be obtained economically. Well Construction Drilling Fluid. The drilling fluid used for the well should provide good hole stability and induce minimal damage to the formation. Depending on the shale-formation mineralogy and stress conditions, the hole can be drilled with freshwater mud, potassium chloride (KCl)-based mud, oil-based mud, or even air.