Engineering

The results of EORI’s sponsored test of Viper Drill’s ultrashort radius (USR) drilling technology could be a sound investment for Wyoming operators.

Ultrashort radius drilling technology was successfully tested in two wells (an injector and a producer) at Thompson Creek Field in northeastern Wyoming that were experiencing problems due to near-wellbore formation damage.  Both wells exhibited marked improvement in performance after the drilling of four short (<30’ long) USR laterals from each borehole, indicating that this method should be considered in other wells throughout the state that are experiencing similar problems.

Development and production of coalbed methane involves the production of large volumes of water. The salinities and sodium adsorption ratios of coalbed methane (CBM) water from the Powder River Basin range from 370 to 1,940 ppm and 5.6 to 69 respectively. Surface discharge of CBM water can create serious environmental problems; subsurface injection is generally viewed as economically nonviable. It has been shown that oil recovery from reservoir sandstones can be improved by low salinity waterflooding for salinities ranging up to 5,000 ppm. There may be both technical and regulatory advantages to application of CBM water to oil recovery by waterflooding. Thin section and scanning electron microscope studies of the mineral constituents and distribution of Tensleep and Minnelusa sandstones show they are typically composed of quartz, feldspar, dolomite and anhydrite cements but have very low clay content. The sands contain interstitial dolomite crystals in the size range of up to about 10 microns. Three sandstone cores from the Tensleep formation in Wyoming were tested for tertiary response to injection of CBM water. The cores were first flooded with high salinity Minnelusa formation brine of 38,651 ppm to establish residual oil saturation. Synthetic CBM water of 1,316 ppm was then injected. Tertiary recovery by injection of CBM water ranged from 3 to 9.5% with recoveries for all but one flood being in the range of 5.9 to 9.5%. Previous studies showed that the presence of clay was needed for response to low salinity flooding. As a test of the recovery mechanism, a Tensleep core was preflushed with 15% hydrochloric acid to dissolve the dolomite crystals. The treated core showed no tertiary recovery or pressure response to CBM water.

Ash Minnelusa Unit Conclusions

• Monitor, monitor, monitor. Make changes based upon reservoir response.
• Improved understanding of the problem improves process application and results
• Volumetric sweep (gels) should be applied before mobility control
• Implement gel processes early for maximum benefits
• Incremental oil expected to exceed 400,000 BBLS (18.4%%5 OOIP) for $0.88/BBL
• Field experience is critical with gel processes. Experience at Ash can be applied to other reservoirs

The purpose of this study was to report on the effectiveness of the Hyperscratcher tool in improving production or injection by cleaning out boreholes that have reported problems with scale, paraffin, or asphaltene build-up.

The Hyperscratcher tool was initially designed and used in California in the 1980s for workovers; as yet it has not been widely used in Wyoming.

Test results show use of the Hyperscratcher Tool significantly improved production in 7 of the 8 wells tested with production improvement varying from 20% to 120%.

Polymer-augmented waterflooding of the Minnelusa in Wyoming has proven to be a successful method for improving production in most cases compared to normal waterfloods. Polymer is a lowcost, low-risk option when considering a method for enhancing production of a particular field. Its primary function is to improve the mobility ratio of the injected water by increasing its viscosity, thereby improving the volumetric sweep and conformance within the reservoir.

Advantages of using polymer include: (1) low cost, (2) preventing early water breakthrough, (3) improving volumetric sweep and conformance, (4) increasing oilwater ratios, (5) mobilizing oil that would likely have been bypassed under normal waterflood conditions, (6) mitigating heterogeneous permeabilities within the reservoir, and (7) other enhanced oil recovery injection technologies can still be applied after the polymer flood. Most, but not all, Minnelusa fields examined exhibited improved recoveries using polymer compared to fields under conventional waterfloods. Uneconomical polymer floods can be caused by a variety of factors, chief of which is the failure to properly understand the internal architecture of the reservoir prior to initiating the flood.

2012 Regional Update on Co2 Conference