Impact of Perforation Deficiency on a Fluid Injection Project - A Case History
Authors: Elkins Lincoln F. , Skov Arlie M. , Liming Hugh F. 
Published: December 2007

Production logging and testing of selected intervals with straddle Production logging and testing of selected intervals with straddle packers indicated that perforation deficiency contributed to low packers indicated that perforation deficiency contributed to low vertical sweep efficiency. Mulitistage perforation fracture treatment with mud cleanout acid, condensate, and wax beads achieved production of oil from 15 to 30 feet of perforations in previously production of oil from 15 to 30 feet of perforations in previously nonproductive permeable sand.

Introduction

Sohio Petroleum Co. is the major working-interest owner and operator of a unitized fluid injection project using an improved recovery method. All project using an improved recovery method. All physical aspects of the reservoir rock and fluids, physical aspects of the reservoir rock and fluids, as well as pressure-production performance during primary operation, indicated that conditions were primary operation, indicated that conditions were favorable for "improved" oil recovery over and above that possible by combinations of gas injection, gravity drainage, and waterflooding. Extensive pre-unit reservoir studies utilized a Hele-Shaw (parallel plate) model to analyze the effects of gravity and mobility ratio on areal sweep efficiency. Also, a "one-dimension" 20-layer computer model without cross-flow was used to investigate the effects of these factors on vertical sweep efficiency for various possible recovery techniques. Analysis also considered analogy with actual waterflood performance in an adjacent fault block. A formation dip performance in an adjacent fault block. A formation dip of 25 degrees to 60 degrees and an average core air permeability of 196 md combine to indicate better sweep permeability of 196 md combine to indicate better sweep efficiency for all oil displacement processes than would be obtained in a similar flatter reservoir. During actual operation. breakthrough of injected fluids into wells offsetting input wells occurred much earlier than anticipated. Injected fluids now have encompassed 15 producing wells up to a maximum distance of 3,000 ft from the nearest input wells. This performance is sufficient to confirm that vertical sweep efficiency at breakthrough has been much less than that expected from the pre-unit studies. In an effort to understand and to control this vertical sweep behavior, we conducted extensive subsurface testing of many injection and producing wells. This included using modern production logging techniques in many wells and separately testing seven different intervals in one observation well using straddle packers. We found that the ineffectiveness of well completion with conventional jet perforation through casing was a major contributor to this poorer-than-expected vertical sweep efficiency. Even poorer-than-expected vertical sweep efficiency. Even in this "clean, homogeneous" sand, the path of the fluid flow through the formation tended to be the same as the intervals where the fluids left the input wells and entered the producing wells. The primary purposes of this paper are as follows:To review the production logging of one well that demonstrated the ineffectiveness of perforations.To outline a perforation fracture treatment cleanout technique used to improve the well completion efficiency.To review subsequent production logging and pressure-production testing that confirmed the pressure-production testing that confirmed the improvement in the producing profile.

Enough of the additional subsurface testing of other wells is included to demonstrate that reservoir heterogeneity controls the over-all fluid movement in this "clean" sand reservoir, a fact that makes thoroughly effective well completions mandatory.

JPT

P. 1063