Predicting Production Outcome From Multi-stage, Horizontal Barnett Completions

Abstract

Abstract Developing a predictive reservoir model involves determination or estimation of key reservoir components, which can vary through the rock volume. Sophisticated, 3-D grid models usually require significant input data and are built for conventional reservoirs producing in Darcy flow. Production from the Barnett shale is not conventional. Shale-rock gas flow involves a complex mixture of free and adsorbed storage and production mechanisms. Free gas can be stored in the microporosity, natural fractures, or thin lamination existing or created during hydraulic fracturing. Adsorbed gas is contained in the organic material randomly distributed in the bulk rock. Horizontal, multistage-fractured wellbores add another level of complexity. Massive hydraulic fracturing of horizontal shale has shown complex fracture networks are created along the wellbore. Mapped data suggests multiple fracture planes are created during injection. These fracture planes can be irregular in length and are not always symmetrical. Conventional reservoir models cannot handle this level of complexity. A new, 3-D, four-phase, nonisothermal, multiwell black oil and "Pseudo-compositional" simulator that allows placement of multiple transverse fractures along the horizontal has been developed. Its ability to model horizontal, multiwing, transverse fractures and account for all three reservoir phases, including injected fluid, makes this model more predictive of production. This paper uses mapped fracture dimensions of horizontal wells in the north Texas Barnett (NTB) to build a reservoir model. Comparisons of model production to real production are made to demonstrate the model's predictive ability. Introduction Horizontal drilling and completion of the NTB began in 1991 and has more than 6,000 horizontal wellbores on production to date. Numerous well construction types and completion strategies that have been investigated in the NTB are listed below.Cemented and uncemented linersCemented production casingProduction casing with mechanical/swell packers and frac portsCemented and uncemented casing using jet-tool perforating and fracturing (East et al. 2004) The most common completion is the cased, cemented production string using the pump down perf-and-plug method of multistage completion (Smith and Starr 2008). Horizontal Completion Design The completion phase of the horizontal Barnett shale is thought to have the most effect on production outcome. Horizontal azimuth for the NTB is usually chosen so that hydraulic fractures created bisect the wellbore in a transverse manner. This option is preferred because it opens multiple fracture planes along the entire lateral length, maximizing the total surface area to flow. Some of the obvious design considerations are:• Lateral length• Fracture spacing or initiation points• Number of stages• gal/ft, lbm/ft• Total gallons and total lbm of proppant per wellbore