Results Of Acid-In-Oil Emulsion Stimulations Of Carbonate Formations

Abstract

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Abstract A low rate, low pressure stimulation technique using a new surfactant retarded, acid-in-oil emulsion has been found effective in providing better sustained production increases than previously obtained in stimulations using 15% and 28% hydrochloric acid in wells having high temperature, low permeability, carbonate formations. A permeability, carbonate formations. A fracturing technique also using the emulsion provided significant initial production provided significant initial production increases, but rapid declines occurred in most wells. The results of 22 treatments using the low rate, low pressure technique and 12 stimulations using the fracturing technique are presented, and are compared to 80 previous treatments using 15% and 28% hydrochloric acid in wells having similar conditions. Introduction Commercial oil production was established on the Cedar Creek Anticline in Southeastern Montana (Central Williston Basin) in 1952, and major development drilling proceeded through 1965. Approximately 640 wells were drilled during this period on the narrow structure which extended for over 100 miles as shown on Figure 1. Major productive zones encountered were carbonates in the Silurian, Mission Canyon, Stony Mountain and Red River formations. The area of interest of this study includes the Pennel, Coral Creek, Little Beaver and Little Beaver East Fields on the southern end of the anticlinal structure. The majority of production in the Pennel Field is from the Red River and Stony Mountain formations while production in the other three fields is production in the other three fields is predominently from the Red River alone. predominently from the Red River alone. With few exceptions, the wells are on 160 acre spacing. Average daily production from the four fields during 1974 was approximately 11,000 barrels of oil per day from 200 producing wells or an average of 55 BOPD per producing wells or an average of 55 BOPD per well. Each field is in a secondary recovery phase with waterfloods installed between 1965 phase with waterfloods installed between 1965 and 1969. MATRIX TREATMENTS USING CONVENTIONAL ACIDS During the early 1970's, Shell performed numerous low pressure, low rate stimulations (here defined as matrix stimulations) using 15% and 28% hydrochloric acid in wells throughout these four fields with modest success. Table I is a summary of the results of all matrix stimulations (a total of 80) that were performed during the period 1971 to 1974. performed during the period 1971 to 1974. Although many stimulations were performed before 1971, waterflood response was not generally noted in these fields prior to this time.