Lateral Water Encroachment In the Pincher Creek Field

Abstract

Abstract Unusual water production performance has occurred in a portion of the Pincher Creek Gas Field. This fingering or ‘lateral water encroachment’ from the downdip aquifer has been insufficient to significantly affect pressure performance, but has severely restricted the productivity of some wells and will reduce the recovery of gas in place. Water encroached into one structurally high drilling spacing unit even before the well was drilled and placed on production. The mechanics of this water movement have been confirmed during two reconditioning operations and by the production performance of wells. It has been found that a watered-out well can be made to produce water-free gas by recompleting LOWER in the same continuously porous interval. Relief from water production after reconditioning may be short-lived. The various factors to which water fingering could be attributed have been examined and are discussed. Lithofacies studies indicate two ‘shoals’ which form one continuous gas reservoir. Premature water encroachment at individual wells could be related to interfingering of rock types and lack of vertical permeability. This water encroachment phenomenon could be effective to varying degrees in other deep, fractured reservoirs in Alberta. INTRODUCTION The Pincher Creek Rundle Gas Pool, located in the extreme southwestern corner of Alberta, as shown on Fig.1, was discovered at a depth of 11,700 feet by the drilling of Pincher Creek No.1 in 1947. Subsequent drilling resulted in twenty-four gas wells and three dry holes. Figure 2 is a structure map which shows the locations of the wells. Commencing early in 1957, the pool was cycled at a raw gas rate of 60 MMcf/D for two years to recover sulphur and condensate. In late 1958, gas sales to Trans-Canada commenced. Water production problems have adversely affected the deliverabilities of wells in the northern half of the field, some occurring very early in the blowdown operation. The primary purpose of this paper is to discuss the unusual water production performance and remedial measures. RESERVOIR CHARACTERISTICS Geology The Pincher Creek sour gas – condensate reservoir consists of a fractured thrust block of Rundle strata striking N3 °W and dipping 4 to 8 degrees to the southwest. The areal extent of the pool is determined by the down-dip aquifer on the west and by faults that bound the eastern edge of the structure, as shown schematically on Figure 4. Two wells appear to have encountered separate fault blocks which are in pressure communication with the main reservoir. The productive portion of the Rundle can be subdivided into five zones, the Upper Dense, Upper Porous. Middle Hard, Crystalline and Lower Porous, each differing in lithology, thickness, porosity and permeability. The five zones form a continuously porous reservoir which is normally 550 feet thick when the entire section is above water and not faulted. In general, the lithology of the pay section is one of dolomite above the Crystalline Zone and of variable amounts of limestone and dolomite through the remainder.