4D Pressure Pilot to Steer Well Spacing in Tight Gas

Abstract

Abstract Obtaining reliable and accurate formation pressures in micro-Darcy rock has been a formidable challenge for tight gas producers. However, it is these pressures that give the most unambiguous data to identify unique reserves. They help to determine the drainage areas as well as appropriate well spacing for tight gas reservoirs. A 4D pressure pilot was designed and installed to measure pressure drop at two observation wells equipped with pressure gauges. The pressure gauges enable pressure monitoring along the wellbore (in space) and over time, hence the name 4D pressure pilot. Two wells were drilled with one in the maximum horizontal stress direction (aligned with the hydraulic fracture azimuth) and one perpendicular to this orientation. Each well was placed at approximately 660 ft from an existing producing well, corresponding to a conventional 10-acre pattern. Twenty pressure sensors were distributed over the 6,000 ft productive interval. One well showed significant depletion in the majority of the sands whereas the other displayed very little depletion. This pressure data together with open-hole and production log data, core data, and geologic models was used to construct detailed static and dynamic models. The resulting history matched models were used to evaluate numerous well densities and patterns. This formed the basis for the two wells per quarter quarter section application for the center of the field, which was approved by the Wyoming Oil and Gas Conservation Commission. Similar data gathering activities have been initiated in other parts of the field to formulate a comprehensive, field-wide spacing plan. Gauge configuration was designed to collect daily pressures in numerous sands without compromising future production. Combining existing systems offered by two contractors into an integrated package mounted external to the casing enabled us to acquire this data, while still allowing for hydraulic-fracture completion and normal production in the future when monitoring objectives were met. Obtaining pressure data with dozens of permanent gauges is expensive, but we are convinced that given the significant impact on estimating gas in place, recoverable gas, drainage area and ultimately well spacing, it is cost effective.