Hydraulic Fracture Diagnostics Used To Optimize Development in the Jonah Field

Abstract

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.

Assessing the Impact of Microseismic Location Uncertainties On Interpreted Fracture Geometries

“…Fig. 5 shows the extents relative to the dataset of σ = 20 m. Note that similar techniques have been used in the literature to measure the volume of the reservoir stimulated during hydraulic fracture treatments 4,6,7 . It is useful to examine this measurement method in the context of the true locations and the true fracture extent.…”

“…This rectangle is a simple graphical representation of the fracture in terms of the distinct length, width and height 4 . The corners of the rectangle are not meant to imply a fracture with sharp corners or any associated stress intensification.…”

“…The hydraulic fracture process results in microseismic emissions, for which the hypocentral locations are computed resulting in a time-lapse image of the fracture growth. The event locations can be used to evaluate the azimuth, height and length of the fracture 4 . Simple, single fracture planes are typically too narrow for the width of the fracture to be assessed from the microseismicity.…”

Stimulating Unconventional Reservoirs: Maximizing Network Growth While Optimizing Fracture Conductivity

“…Most published results of fractures in tight sands (7)(8)(9)(10)(14)(15)(16)(17)(18)(19) tend to support this assumption, as shown for example by Wolhart et al (10) in several Piceance basin tests. Nevertheless, there is a wide variation in microseismic behaviour observed in such tests.…”

Source-Mechanism Studies on Microseismicity Induced by Hydraulic Fracturing

“…Microseismic mapping is a technology that has proven valuable for monitoring stimulations in unconventional reservoirs, such as gas shales and tight-gas sandstones (Hart et al 1984;Warpinski et al 1990;Walker et al 1998;Fisher et al 2002;Maxwell et al 2002;Griffin et al 2003;Fisher et al 2004;Warpinski et al 2005;Cipolla et al 2005;Mayerhofer et al 2005;Wolhart et al 2005;Wolhart et al 2006;Shemeta et al 2007;Vulgamore et al 2007;Daniels et al 2007;King et al 2008;Potapenko et al 2009;Waters et al 2009). It is performed by fielding a large array(s) of highly sensitive and high-frequency-response three-component geophones or accelerometers in an offset well(s) in close proximity to an interval that is being stimulated.…”