Integration of Laboratory and Field Data for Development of a CO2 Pilot in the Naturally Fractured Spraberry Trend
Authors: Schechter David S. , McDonald Paul , Sheffield Tom , Baker Richard O. 
Published: December 2007

This paper provides an update for an ongoing CO2 pilot in the naturally fractured Spraberry Trend in West Texas. We presented reasoning and evidence that stimulated interest in attempting CO2 injection into this depleted, ill-characterized reservoir. A self-evident conclusion was that the natural fracture system, although universally accepted as dominating all aspects of production behavior in Spraberry, is not well characterized and needs to be rigorously understood before any attempt at process modeling could be attempted. The tremendous area that the productive sands cover also raises questions concerning the relation of these widely occurring fractures to basin-wide tectonics.

In this manuscript, we present coring results from the central production well in the 15-well pilot. In addition, we discuss laboratory results and future plans to integrate this data for development of successful process options.

Coring the E.T. O'Daniel #37

The E.T. O'Daniel #37 is the central production well in the projected 15 well pilot project as shown in Fig. 1. This well was sponge cored in the main 5U pay interval. The objective of the sponge core was to determine current oil saturations with a secondary objective of encountering natural fractures.

The following procedure was followed for the central production well:Sponge core the main 5U pay zoneOpen-hole loggingFormation Micro Imaging logComplete, stimulate and produce until steadyShut-in for pressure build-up testPulse test with existing wells

Core was retrieved from the majority of the Upper Spraberry, although difficulties were encountered and only rotary sidewall cores from the 1U pay zone were retrieved. Acquisition of this core reaffirmed our earlier analysis of previous core wells, that the net pay in the Upper Spraberry primarily consists of two thin (8-15 ft each) pay zones, the 1U and 5U. Sharp contrasts are observed by fluorescence between shales containing no oil and the 1U and 5U pay zones, a fine silt with a very low clay content. The 1U and 5U pays zones are easily identified by integration of whole core analysis and open-hole logs into standard shaly-sand algorithms.

The E.T. O'Daniel #37 was perforated and stimulated in the 1U and 5U with 55,986 gallons of 30 lb. X-link delayed borate and 152,260 lbs. of 20/40 mesh sand. The well was produced (average of 11 bopd) until steady and is currently shut-in for a build-up test. After the pressure test the central production well will be pulsed while listening in current wells surrounding the pilot area, shown in Fig. 1. This test will confirm whether or not the near well-bore orientation data that suggests a predominant east-west fracture orientation extends into the interwell region.

Fracture Description

Several natural and drilling-induced fractures were encountered in the 5U pay zone, occurring from 7220–7236 ft. Whole diameter samples were taken for paleomagnetic orientation. Results of core observations along with the interpreted FMI log are shown in Fig. 2. Fractures were oriented approximately N85 E. Agreement was excellent between the orientation resolved by the FMI log and the paleomagnetically oriented whole core.

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