In December 1929, with the nation gripped in the grim beginnings of the Great Depression, Deep Rock Oil Co. struck crude at a depth of 4,345 feet in the mesquite- and sand shinny-dotted high plains of Andrews County, Texas. Since that time, Andrews County has produced more than 2.5 billion barrels of oil from prolific reservoirs perched on the Permian Basin's broad Central Basin Platform. Indeed, in 1956 Andrews made 60 million barrels of oil and ranked as the most productive county in the nation. The glory days of Andrews are not quite past, however. Some 20 years ago, major oil companies began to discard their great Permian fields and smaller producers moved into the landscape. The independents diligently tried to extract the value that remained in the largely depleted properties. Today, high oil prices, new technologies and skilled operators and determination are combining to wring even more production from this vintage corner of America's oil heartland. Andrews County posted a production increase of nearly 300,000 barrels of oil in 2005 over 2004, closing out the year at 23.6 million barrels. One company that has been contributing to that incline is Fort Worth-based Range Resources Corp., which has raised production in its West Fuhrman-Mascho Unit in Andrews County from 290 barrels a day in May 2002 to 3,400 barrels per day at present. And it's accomplished this in a field that has been producing since the 1940s. Range's 3,700-acre property sits on the west side of massive Fuhrman-Mascho Field. Just its unit alone has made some 12 million barrels of 35-gravity crude. Most of the oil has been pumped from the Permian San Andres, a shallow-water carbonate formation; the Grayburg sandstone has contributed secondary volumes. A latent opportunity Range acquired the West Fuhrman-Mascho property in 1997, but didn't start major investments immediately. "We drilled 10 wells when we first bought the asset, but oil prices were very low at that time and we couldn't justify additional work," says George Teer, vice president of operations, Permian division. The company tabled its program until 2002, when prices had improved. Range began its redevelopment with a detailed geological and petrophysical study of the San Andres and Grayburg formations. "Permeabilities in the San Andres range from micro-millidarcies up to 100 millidarcies," says Tommie Wilson, a former Missouri School of Mines professor currently under contract with Range. "In our area, porosities average 9% to 10%, and the gross interval is 250 to 300 feet." Individual wells reach the reservoir at depths between 4,300 and 4,600 feet and encounter between 40 and 150 feet of net pay. "When we bought the property, we recognized that it had tremendous resource potential. Only 8% to 10% of the original oil in place had been recovered," says Teer. Range was intrigued for several reasons. The major firm that operated the property in the past had installed an unsuccessful waterflood in the 1970s that suffered from premature water breakthrough. Range thought the failure of that attempt and the discontinuous nature of the reservoirs meant pockets of unproduced oil likely remained throughout the unit, particularly in the San Andres. "The original waterflood used an inverted nine-spot pattern, which immediately watered out every east-west producer," says Teer. In addition, out-of-zone injection severely hampered the recovery efforts. The major operator subsequently shut down the flood and sold the unit in the late 1980s. Range also saw potential for infill drilling, as the unit had been developed on 40-acre spacing, while a number of neighboring San Andres fields were infilled to 20-acre spacing or less. The independent reinitiated water injection in 2002, converting the original waterflood to an east-west line drive on a much denser spacing. It reduced spacing to 20 acres, and last year received approval from the Texas Railroad Commission to infill to 10 acres. "We try to put as much water in the ground as we possibly can, while staying out of the Grayburg," says Wilson. No significant water breakthrough has occurred to date. The reduced spacing permits the recovery of otherwise unrecoverable oil trapped in the discontinuous porosity and permeability. It also improves the control and efficiency of water injection and waterflood recovery. Since 2002, Range has drilled 126 producers and 17 injectors in the field and injected 13.4 million barrels of water. It currently has 199 production wells and 23 water-injection wells on the property. Its average wells are completed at rates of 130 barrels per day, at a cost of $480,000. Some of the new wells have pleasantly surprised Range, posting initial rates of 300 barrels of oil per day or more, which is comparable to wells drilled early in the field's life. In addition to intensive drilling and repressurization efforts, Range also has modified the completion and frac techniques. The original wells were drilled openhole into the San Andres and shot with up to 900 quarts of nitroglycerin, says Pat Stevens, district engineer. In the 1960s and '70s, the operator re-treated the wells with sand fracs. During the 1980s, 150,000-pound fracs were used, with sand concentrations of up to 10 pounds per gallon. "These fracs created short, highly conductive fractures," he says. "The initial rates were high, but the wells dropped off very rapidly." Range's approach is to complete the entire San Andres with a single-stage 200,000-pound frac job with sand concentrations up to 5 pounds per gallon. "We get much longer frac lengths, and we still have enough conductivity to drain the reservoir." This technique has not only improved results, it has also shaved three days off each well's completion time. Moreover, Range is refracing inactive wells and returning them to production. It estimates that a recompletion of each old well yields 20,000 barrels of incremental reserves. To date, the company has refraced more than 40 wells, at a cost of $150,000 per well (if mechanical problems are not encountered). Unfolding potential Currently, Range is mounting a three-pronged approach in the unit: drilling new wells, expanding the waterflood and refracing existing wells. "We have 81 wells to drill this year, and another 25 to 30 producers to drill after that," says Teer. For the past two years, Range has been running one drilling rig in the field, and it plans to add a second rig this year. The waterflood is also being expanded to a new portion of the unit. Range has been operating a pilot waterflood in Section 18 for the past three years, and will expand that into sections 23 and 24. "Beyond that, the flood could be expanded over an area another two to three times its present size." The waterflood should be able to recover another 4% to 5% of the original oil in place. "At this point in time, we see numbers of 210- to 220 million barrels of oil in place in the San Andres formation in the unit," says Wilson. Tertiary recovery is a possibility down the line as well, and an existing CO2 line conveniently bisects the field. In addition, Range holds two additional units in the area. Its Block 10 and Northeast units also produce from the San Andres. "We've been concentrating on West Furhman, but we plan to spend more time and money on our other units in the future," says Teer. And, other operators in the area are emulating Range's success with infill drilling, refracing and pilot waterflood programs of their own. So despite its aging reservoirs, there's still a lot of oil to be produced from Andrews County.