The Madison reservoir in LaBarge Field in Wyoming, U.S.A., is a multi-zone carbonate on the crest of a regionally plunging anticline. It is ~800 ft thick, covers more than 1,000 square miles, includes 4,000 ft of structural closure and holds 22 TSCF initial methane in-place. Methane percentage varies from a high of 23% at the crest to a low of 5% near the gas-water contact, with inerts - CO2, N2, H2S and He - making up the remaining gas. ExxonMobil is the only operator producing from LaBarge Madison and has built a dedicated gas plant to monetize the resource. Current production is 700 MMSCF/d (150 MMSCF/d methane) with 16 crestal producers and two downdip injectors re-injecting 60 MMSCF/d acid gas into the Madison aquifer - one of the world's largest acid gas re-injection projects.

Key project objectives are to:

  1. maximize methane production from the existing wells,

  2. efficiently operate the gas processing plant, and

  3. ensure sufficient acid gas disposal capacity such that production is not constrained.

Key reservoir and operational uncertainties include (1) the detailed initial distribution of methane vertically and areally, (2) the impact of the mountainous topography on surface facility flowline hydraulics and producer performance, and (3) long-term injectivity, movement and containment of the injected acid gas within the aquifer.

This paper discusses the integration of reservoir characterization studies, geochemical analysis, surveillance data, reservoir simulation and surface facility network models to optimize the near-term development plan and evaluate potential expansions. Key subsurface results presented include:

  1. a potential explanation for the large gas compositional gradient and the history-match approach used to approximate the methane distribution and

  2. a method to incorporate temperature-dependent acid gas injector wellbore hydraulics and acid gas viscosity in order to more accurately model pressure and fluid flow.

Integrated reservoir and facility modeling led to selection and implementation of large bore tubing workovers that are, in most cases, more economically attractive than new drillwells.

Field Overview

LaBarge Field is located in Sublette County in southwestern Wyoming, U.S.A., as shown in Figure 1. ExxonMobil owns and operates a majority of the leased acreage, as shown in Figure 2. The primary pay interval is the Madison formation, a deep Paleozoic Mississippian carbonate reservoir, composed of anhydrite and dolomite sequences interbedded with limestone. The Madison reservoir has an original in-place methane resource of 22 TSCF (3.7 billion BOE) distributed over more than 1,000 square miles, and is normally pressured. Methane composition varies from 23% on the crest to only 5% near the gas-water contact.

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