Combining Acid Fracturing, Propellant Stimulations, and Polymer Technologies to Develop Additional Reserves
Authors: Hall F.R. , Whisonant R.J. , Woods M.E. 
Published: March 2010

The continuing use of combined crosslinked polymer, propellant, and acid fracturing treatment technologies has resulted in additional reserve development in a mature waterflood field in Wyoming. These three technologies have been used in combination on over 40 wells during 1996 and 1997 in the Oregon Basin Field, located in Park County, Wyoming, USA.

The first use of Acrylamide-polymer/CrIII-carboxylate (gel) Technology(1) in Oregon Basin took place in the mid-1980s. The treatments were used to reduce water production in producing wells and improve both vertical and areal conformance in injection wells. Acid stimulations have been used since the 1940s as a means of improving production, with the first acid fracturing treatments being pumped in the late 1980s. Beginning in 1996, these two technologies were combined in an attempt to successfully increase oil production from wells that had not been considered acid stimulation candidates due to their total productivity. Propellant was used as a perforation breakdown technique after pumping the gel treatment and prior to the acid stimulation.

This paper discusses the evolution of the gel and acid fracturing treatment designs, and the reasons for combining the two treatment techniques. The results of the 1996 - 1997 program are discussed in detail, as well as the changes in treatment designs that have taken place during the project. Data is presented that confirms accomplishment of the treatment objective.

Introduction

One of the primary producing zones in Oregon Basin, the Embar formation, is a carbonate in which the lower portion of the interval is more highly fractured and of higher porosity than the upper portion of the interval. Processed openhole logs from recent infill wells (Figure 1) indicated that the lower portion of the interval had been depleted to a much lower oil saturation than the upper interval. This differential depletion is believed to be attributable to significant vertical permeability variations and inefficiencies in the waterflood. Rock property variations and natural fracturing within the interval have made it difficult to effectively stimulate the upper portion of the pay interval. This has also contributed to the ineffective depletion of the zone.

Gel treatments have historically been successful in reducing adverse channeling from injection to production wells and in reducing water production in producing wells. The treatments have generated significant incremental reserve development over the life of the field. Acid stimulations have also made a significant contribution to reserve development in Oregon Basin. These treatments have evolved from small volume "matrix" type treatments in the 1940s to larger volume acid fracturing treatments in the late 1980s. Foam fracturing has been used in the past few years, utilizing gravity segregation concepts to more effectively stimulate the upper, less depleted portion of the pay interval(2).

This paper describes the continuing use of the combined gel, propellant stimulation and acid fracturing technologies that have been used in Oregon Basin since 1996. The combination of these technologies has resulted in significant reserve development and has been applied to both production and injection wells(3).