Awakening an Old Field—A Case Study of a Refracturing Program in the Greater Green River Basin

Abstract

Summary Restimulation of wells completed in the Frontier Formation, a low-permeability (e.g., 0.01-0.05 md) gas sand, has proved to be successful in the Fontenelle Field. The field is east of the Fontenelle reservoir, on the LaBarge Platform in the western part of the Greater Green River Basin in southwestern Wyoming. In this area the majority of hydrocarbon reserves in the Second Frontier are produced from the massive shoreface sandstones locally known as the Second Bench of the Second Frontier (Kf22b). To date, Berco Resources, LLC has increased reserves in the Fontenelle Field by restimulating four wells producing from the Frontier Formation with massive hydraulic fracturing treatments. Because of the success of these treatments, another operator in an offset area to the north has also successfully implemented a Frontier refracturing program. This paper summarizes the refracturing program and the success which Berco Resources, LLC has realized. The candidate selection process is examined, as well as operational considerations when restimulating old wells. The stimulation treatments and fluid systems are also investigated. Daily/monthly production data consisting of gas, condensate, and water rates along with well head pressures are evaluated for all cases with fractured well type curves, the pseudoradial flow specialty plot (?p/q vs. log t), and a production simulator comparing actual versus modeled production rates. Finally, the impact of the refracturing treatments on economic return is presented. The success of the refracture treatments has led to a new drilling/completion program in the Fontenelle Field in 2006 by an operator that recently acquired the Berco Resources, LLC properties. Introduction Field Description. Fontenelle Field is approximately 75 miles northwest of the town of Rock Springs, Wyoming (Fig. 1), on the southeast end of the LaBarge Platform. The field, positioned primarily in T26N-R112W, T25N-R111W, and T25N-R112W, encompasses nearly 120 square miles in both Lincoln and Sweetwater counties. To date, production from the Fontenelle Field has been 271.77 Bcf gas and 525,563 barrels of oil from 343 wells. Production has come mainly from the Second Frontier, but thin marine sandstones in the overlying Baxter Formation have produced locally. Geology. Deposition of the Cretaceous Second Frontier Formation, in the Fontenelle area, began as lower delta plain muds, carbonaceous shales, coals, and fluvial sands prograded over the poorly developed Third Frontier shoreface facies, which represented the culmination of the Mowry transgression. Sixty to seventy feet of lower delta plain sediment was deposited before a relative rise in sea level flooded the lower delta plain environment. This resulted in an abrupt change from the lower delta plain mudstones, siltstones, and shales to offshore marine mudstones and siltstones. This transgression marked the beginning of deposition of a thick, wave dominated shoreface sequence which prograded eastward into the Cretaceous Interior Seaway and contains the majority of the gas reserves in this part of the LaBarge Platform. This shoreface sequence is known as the Second Bench of the Second Frontier (Kf22b). Gas production in the Fontenelle area comes primarily from the Second Bench of the Second Frontier (Kf22b). This shoreface sequence consists of a 30 to 60 foot thick section that grades upwards from a very fine grained, bioturbated sandstone to a more winnowed, medium grained sandstone. The top of the bench often contains a very clean, high resistivity sandstone that varies in thickness from zero to 20 feet. This is interpreted to be a clean, medium grained sandstone deposited by distributary channels that have cut into the underlying shoreface section. Permeability in these channels is generally an order of magnitude better than the underlying shoreface section. The thick shoreface sandstone is capped by the mudstones and carbonaceous shales of the lower delta plain environment. The Frontier Formation, in the Fontenelle area, conformably overlies the marine Mowry Formation and is conformably overlain by the marine Baxter Formation (Robertson and Broadhead 1993). It is Cretaceous in age and extends from upper Cenomanian to upper Turonian.