This paper reports on a study conducted to assist with field development in the Jonah Field in Wyoming. Microseismic and surface tiltmeter fracture mapping was performed on ten wells in two areas of the field and over 100 fracture treatments were mapped. The fracture mapping study was performed as part of a pilot project to evaluate ten-acre well spacing. The Jonah Field is located in the Green River Basin in Sublette County, WY. Production is primarily from over-pressured and tight sandstones of the Lance Formation. The Lance in Jonah consists of many stacked low permeability sandstones. Due to the low permeability, stimulation is required for economical production rates. Gross pay intervals vary from 2,800 ft to 3,600 ft and wells are stimulated in multiple fracture stages. Each fracture stage may target three to six sands with eight to twelve total stages for each well. The study shows mapping results for fracture treatments in both mapping areas. Fracture length was longer than expected and varied somewhat by stage. Some stages were contained but for many stages there was significant height growth and treatment overlap. Fracture complexity was observed which could be due to natural fracturing, faulting, depositional heterogeneity and depletion. These fracture mapping results are being combined with geologic, geophysical and engineering data from the field to assist with field development. This paper details the results of the mapping and discusses issues with well placement, stimulation design and treatment staging identified by the study. Overview of the Jonah Field The Jonah Field1–5 is located in Sublette County, WY approximately 70 miles north of Rock Springs as shown in Figure 1. The field is a large, structurally complicated wedge shaped fault trap located in the northwestern part of the Green River Basin as shown in Figure 2. Production is primarily from over-pressured and tight sandstones in the Cretaceous Lance Formation. The Lance formation in Jonah Field is composed of a stacked sequence of 20 to 50 fluvial channel sands inter-bedded with associated over-bank siltstone and floodplain shale deposits. Gross interval thickness ranges from 2,800 ft to more 3,600 ft. Within this interval the net-to-gross ratio varies from 25% to 40%. Sandstone bodies occurs as individual 10 ft to 25 ft thick channels and stacked channel sequences greater than 200 ft in some cases.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper reports on a study conducted to assist with field development in the Jonah Field in Wyoming. Microseismic and surface tiltmeter fracture mapping was performed on ten wells in two areas of the field and over 100 fracture treatments were mapped. The fracture mapping study was performed as part of a pilot project to evaluate ten-acre well spacing.The Jonah Field is located in the Green River Basin in Sublette County, WY. Production is primarily from overpressured and tight sandstones of the Lance Formation. The Lance in Jonah consists of many stacked low permeability sandstones. Due to the low permeability, stimulation is required for economical production rates. Gross pay intervals vary from 2,800 ft to 3,600 ft and wells are stimulated in multiple fracture stages. Each fracture stage may target three to six sands with eight to twelve total stages for each well.The study shows mapping results for fracture treatments in both mapping areas. Fracture length was longer than expected and varied somewhat by stage. Some stages were contained but for many stages there was significant height growth and treatment overlap. Fracture complexity was observed which could be due to natural fracturing, faulting, depositional heterogeneity and depletion.These fracture mapping results are being combined with geologic, geophysical and engineering data from the field to assist with field development. This paper details the results of the mapping and discusses issues with well placement, stimulation design and treatment staging identified by the study.