Trends In Unconventional Gas - Halliburton

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D r i l l i n g & Pr o d u c t i o n be efficiently fractured independently by: • Using coiled tubing or tubulars with hydrojetting techniques. • Using dynamic diversion techniques for either vertical or horizontal placement. • Or, incorporating completion mechanical downhole assemblies featuring stimulation sleeves and swellable elastomer packers to enable stimulation of multiple zones without use of bridge plugs to isolate intervals to be treated. These pinpoint stimulation techniques offer operators cost-effective methods to stimulate multiple zones in one rig-up. Fluid treatment Ultralow permeability is the primary challenge in shale formations. Fracturing fluids that are nondamaging and that enhance load recovery is essential in shale formations with very limited permeability. A combination of specialized chemistries delivers maximum effective fractures and preserves the formation’s existing permeability to gas, contributing significantly to the shaleproduction success. Components of the fracture fluids include: • Special friction reducers formulated to reduce potential fracture-face damage caused by long-chain polymers, without compromising their capability to reduce friction pressure. • Microemulsion surfactant that helps reduce capillary pressure, releasing imbibed treatment water and improving gas permeability. It also provides significant safety and environmental benefits by replacing methanol in water-block treatments. • Fracture-cleaning enhancer and conductivity enhancer for accelerating fracture cleanup and flowback of treatment fluids. Together, these components create a synergistic fluid treatment solution designed to help optimize gas production from formations with ultralow native permeability. The system provides workable, cost-efficient solutions for shale productivity programs from beginning to end—from analysis and planning to drilling, fracturing, early production, long-term production, and ultimate recovery/abandonment. The ability rapidly to fracture multiple independent zones yields a significant decrease in completion time. The components of the system work Makeup of productive shale formations In general, a productive shale formation includes these characteristics: • Zone thickness >100 ft. • Well bounded and containing energy. • Maturation in the gas window: R o = 1.1 to 1.4. • Good gas content >100 scf/ton. • High total organic content (TOC) >3%. • Low hydrogen content. • Moderate clay content
improves environmental and safety performance by replacing methanol; and is effective in reservoirs with matrix permeability in the nano-Darcy range. Formation damage A new friction reducer helps reduce fracture-face damage from long-chain polymers. The maximum horsepower can be applied in a shale formation rather than being wasted just to get the fluid through the mechanical system. Because this reducer contains no phenols, it provides improved environmental performance and exhibits less flocculation than conventional friction reducers. A viscosity-reducing agent helps maximize the effectiveness of water-fracturing treatments by reducing fluid viscosity, improving load recovery, minimizing frictionreducer polymer damage, and preventing polymer adsorption to the fracture face, thereby enabling improved production. These purpose-focused technologies provide a holistic and economical approach to bringing forth energy from unconventional shale resources. Two cases demonstrate the use of the shale production system (SPS): • Case 1. A horizontal shale well was stimulated at four intervals with stimulation sleeves sequentially to isolate each interval of interest during treatment. The four intervals were fractured in 15 hr, placing 1.2 million lb of proppant with 2.3 million gal of fluid in a continuous operation. Normal stimulation practices would have required 2 days to run four traditional fracturing stages. The operational efficiency gained through the use of the stimulation-sleeve process reduced completion costs by 15-20%. • Case 2. Gas sales from six Barnett shale wells were compared after three of the wells had been treated with SPS additives and three were treated without additives. First gas production was quicker in the three wells treated with SPS additives and these wells produced 100% more gas sales/day. The Mississippian Barnett shale serves as source, seal, and reservoir in a world-class unconventional natural gas accumulation in the Fort Worth basin of northcentral Texas. The Barnett is lithologically complex, with low permeability, and requires artificial stimulation to produce. 1 • Case 3. Ten horizontal shale wells Shale technologies Several production-enhancement processes are useful in shale-gas reservoirs: • Prospect evaluation and core testing. • Shale lithotyping to determine key characteristics of productive shale. • Log data integration and analysis specific to shale. • Designing and drilling the vertical and horizontal well for stimulation. • Proppant size and loading considerations. • Optimization and tailoring water-frac fluid chemistry to the shale. • Remedial treatment processes for obtaining long-term sustained production. in Oklahoma were recently completed with massive slick-water fracturing. Four of these wells were fractured with microemulsion surfactant (MS) and six wells did not have the MS treatment. The MS treatment reduced water saturation and capillary pressures along the fracture faces, which improved relative permeability to gas. Wells using the MS service had initial gas production among the best wells in the field. Life-cycle phases Operators producing gas from shale reservoirs can be more successful by following the five life-cycle phases of project development and carefully choosing technologies appropriate for each project phase: 1. Reservoir assessment. Evaluate shale and reservoir potential. 2. Start-up exploration. Drill experimental wells and investigate fracture design and production prediction. 3. Early development (mass production). Rapidly develop using an optimized design. Develop database and benchmarks. 4. Mature development (reserve harvesting). During this cash-flow cycle, match production histories; adjust reservoir model; image database. 5. Declining phase (maintenance and remediation). Identify remedial candidates, restimulate, initialize lift mechanisms and conformance methods. (Similar coalbed methane life-cycle phases are discussed in the final article in this series. 2 ) Prospect evaluation Usually, the first step in the design and application process is to evaluate the shale prospect. Initially, both 2D and 3D seismic data are processed to determine the extent of the shale play. The volume of shale is estimated in tons/acre (ton/acre-ft). Gas in place (GIP) is calculated from the geochemical determination of standard cubic feet/ton (scf/ton), as follows: GIP = (ρ)(1,359)(scf/ton) = scf/acre-ft. Shale samples collected from various sources help in determination of the commercial viability of the project. Factors include: • Shale hydrocarbon content (scf/ ton, bbl/ton, GIP). • Shale maturity. • Kerogen type (Types I and II, oil; Type III, gas). • Shale porosity, permeability, oil, water, and gas saturations. • Shale desorption constant, or gas isotherm. • Shale bulk density, ρ (g/cu cm). Log data requirement A triple-combo log can be used to obtain density, gamma ray, resistivity, neutron, and density porosity.
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Trends In Unconventional Gas - Halliburton

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