Abstract

A detailed review of 69 acid stimulation jobs completed from 1984 through 1986 in the Inglewood field, California led to mechanical and chemical improvements that dramatically increased production response to acidizing. Average peak oil production gain from stimulation has increased from 22 to 45 bopd using the improved system. Significant procedure changes introduced in late 1987 included using a 40 foot circulation wash tool, overflushing acid immediately and modifying the stimulation chemicals. Damage mechanisms being treated are:

  1. calcium carbonate scale;

  2. asphaltenes and paraffins;

  3. migrating clays and formation fines, and

  4. drilling and completion fluid damage caused while gravel packing.

Introduction

A Lotus spreadsheet was created with data from each stimulation job completed in 1984 to 1986 using well records and production curves. Data was recorded on production curves. Data was recorded on worksheets and transferred to the spreadsheet that was used to manage and sort the information. Figure 1 shows the spreadsheet headings and data collected for one example job.

Cumulative incremental oil gain was used as a measure of job success instead of daily oil rate increase. High initial oil rates after stimulation sometimes decline rapidly, making incremental oil gain a more objective measure of success. The spreadsheet was sorted from highest to lowest cumulative oil gain. Several job variables were plotted against cumulative oil gain to look for trends indicating the most productive job design. Job costs and economic justification were reviewed, but are not included in this paper.

Stimulation procedures and chemicals were studied and compared to the Petroleum Engineering literature with particular respect to Inglewood oil, water and core analysis. Samples obtained during well pulling operations were analyzed for pulling operations were analyzed for insight into damage mechanisms. The study findings and possible improvements were discussed with Inglewood Production Engineers and Foreman, contract Toolpushers, wash tool service men, acid pump operators, in-house experts and acid service company chemists.

Several changes in stimulation chemicals were implemented. Exclusive use of the long spaced circulation wash tool designed in Inglewood was begun. Production response to the new stimulation process was evaluated.

INGLEWOOD FIELD BACKGROUND

The Inglewood field covers some 1200 acres located about ten miles west of downtown Los Angeles, Figure 2. It consists of three reservoirs under active waterflood and four reservoirs under primary depletion, Figure 3. The Vickers and Rindge waterflood zones are the subject of this paper because they are the most prolific paper because they are the most prolific zones. Waterflooding in Inglewood began in 1954 and is in mature stages throughout the field, average watercut is 96%.

P. 673

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