This paper presents a new approach for determining OGIP early in the field life of an edge-water drive gas reservoir. The approach is applied to Ballycotton gas accumulation. Ballycotton was discovered in March 1989 adjacent to the nearby Kinsale Head Field, a major gas accumulation in the Celtic Sea, Ireland. Ballycotton and Kinsale Head have a common aquifer. Kinsale Head Field was put on production in 1978 using two platforms Alpha and Bravo. From July 1991, Ballycotton produced gas as a subsea-completed satellite of the Kinsale Head Field, tied back to the Bravo platform at Kinsale Head. A permanent gauge was installed on the subsea tree in 285 feet of water. Using continuous pressure and rate measurements, we routinely interpreted well data using superposition techniques. Within the first six months of production, an accurate estimate of original gas-in-place (OGIP) was established from the data. This is in contrast to the p/z versus Gp material balance approach, which is seldom accurate early in the life of the field.

This case history clearly illustrates the benefit of utilizing continuously measured pressure and rate data to obtain an accurate original gas-in-place early in a field's life. In addition, this paper demonstrates the benefit of permanently installed pressure gauges in subsea-completed satellite fields.

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