VICKSBURG FAULT ZONE FIELDS
VICKSBURG FAULT ZONE FIELDS. The Vicksburg Fault Zone fields produce oil and gas along a trend that stretches north and northeast from the Mexican border across Starr, Jim Hogg, Brooks, Jim Wells, Kleberg, and Nueces counties of South Texas. The most prolific main fields of the trend are located on the southern and northern ends of the fault, leaving the middle without significant production. The typical main field consists of twenty to forty oil and gas producing, compartmentalized reservoirs, but some areas have hundreds of these faulted zones. The Railroad Commission separates each main field into zone fields, representing each producing compartment. Production from individual zone fields appears insignificant, but the combined cumulative yield from its numerous zones makes a main field significant. The significant main fields of the trend, running from south to north along the fault, include Garcia, Rincon, Sun, and Kelsey in the southern area. The northern area has La Gloria, Tijerina-Canales-Blucher, Seeligson, Borregos, Stratton, Agua Dulce, Richard King, and Wade City fields. The oil-bearing trend consists of two plays, producing from depths of 3,800 to 7,100 feet in Frio and Vicksburg sandstone fluvial and deltaic systems. The shallow play is found on the southern end of the fault and gives up oil from immense rollover anticlines. The deep play taps production from complex, large-displacement faults. The main fields of the oil trend were discovered from 1928 through 1945. In many deeper areas the Vicksburg sands produce gas rather than oil.
The first major main field to produce oil on the fault was Agua Dulce in Nueces County at the northern end of the trend. It was discovered at 4,836 feet in April 1928. Although the field had no one reservoir that held more than ten million barrels of oil, its many zone fields yielded a combined cumulative total of more than 53.7 million barrels of oil by 1994. Without an impressive reservoir, the field caused little excitement and further development of the Vicksburg trend moved slowly. It was November 1937 before additional main fields were opened, and exploration remained on the northern end of the Vicksburg Fault Zone. Those fields were Seeligson in Jim Wells County, producing at 5,350 feet, and Richard King in Nueces County at 5,400 feet. Seeligson field and its various zones eventually became the largest volume producing area in the trend and by 1994 reported a combined cumulative yield of more than 272.7 million barrels of oil. In 1938 exploration along the fault zone increased, and four main fields were brought in. Rincon field in Starr County found oil at a depth of 4,000 feet and became the first field on the southern end of the fault zone. Its cumulative yield along with those of its abundant zone fields totaled more than 75.4 million barrels of oil by 1994. Stratton field in Kleberg County, the second discovery for the year, drew production from a depth of 6,500 feet and moved the focus of exploration back to the north. In combination with its zone fields, Stratton area reported a cumulative total in excess of 95.5 million barrels of oil by 1994. Kelsey field in Jim Hogg County encountered oil at 4,730 feet and defined the northernmost edge of the southern fields. Its zones and main field gave up a cumulative figure that exceeded 116.2 million barrels of oil by 1994. The fourth field located in 1938, Sun in Starr County, filled the gap between Kelsey and Rincon fields when it began producing from a depth of 4,858 feet. The various Sun zones pushed its combined cumulative yield to nearly 52 million barrels of oil by 1994. In 1939 exploration concentrated on the area south of Seeligson field, and La Gloria field in Brooks County came into production at a depth of 6,560 feet. With its zone fields, the La Gloria area reached a cumulative yield of over 31.5 million barrels of oil by 1994.
Although five main fields were found on the fault in 1938 and 1939, those fields were discovered as explorationists used seismograph, torsion balance, and magnetometer to step out from proven areas to drill. No attempt had been made to form an overview of the widely-scattered field developments until November 1939. At that time geologists Alexander Deussen and K. D. Owen described the Vicksburg Fault Zone as a structural belt that extended across South Texas and paralleled the coast, associated with anticlines, faults, unconformities, and sand wedges that formed traps for oil and gas accumulations. With the trend characterized and with its potential for oil and gas production recognized, three important fields were introduced in 1940. Two of the new fields were located in the Rincon area of Starr County-Rincon Frio D-5 (3,800-foot depth) and Rincon E1, E2 (4,000-foot depth). The third area of discovery was the main Wade City field (4,800-foot depth) in Jim Wells County. Five significant fields came on line in 1941. They were Kelsey M-2 (4,730-foot depth, Jim Hogg County), Sun Frio D-1 (4,300-foot depth, Starr County), and three zones in the Seeligson area of Jim Wells County-Zone 14-B (5,073-foot depth), Zone 19-C-4 (5,853-foot depth), and Zone 20-C-01 (6,090-foot depth). In 1942 a new main field was brought into production along with two Seeligson zones. They were Garcia Main (3,800-foot depth, Starr County), Zone 16 (5,675-foot depth, Jim Wells County), and Zone 19-B (6,089-foot depth, Jim Wells County).
Although no significant new fields were added in 1943, two zone and two main fields were located in Jim Wells County in 1944. They were Seeligson Zone 10 (4,592-foot depth), Blucher 21-B (7,109-foot depth), Tijerina (7,190-foot depth), and Canales (7,221-foot depth). In 1945 the last main field on the fault was brought in when Borregos began producing (6,889-foot depth, Kleberg County) and eventually spawned eighty-seven zone fields. Of the zone fields discovered in the 1940s the most prolific in cumulative barrels of oil by 1981 were Seeligson Zone 19-C-4 (80 million), Tijerina-Canales-Blucher 21-B (77 million), and Seeligson Zone 14-B (30 million). Even though the most prolific oilfields were found in the 1930s and 1940s, development of the oil play continued through the 1950s and into the 1990s with more zone discoveries. The gas play attracted operators in the late 1940s and persisted into the 1990s, as operators drilled to depths of 7,000 to 12,000 feet on the fault. Even with the growing interest in gas exploration, some operators still flared casinghead gas in South Texas fields as late as March 17, 1947. On that date the Railroad Commission reacted to a gas-flaring violation in Seeligson field by shutting in production until a cycling and compression plant was completed to process gas. With gas-flaring permanently ended by the 1950s, operators located most of the gas fields in the trend during the 1960s and 1970s. Gas production in Vicksburg sands consists of twenty-five main fields that produce from seventy-five immense reservoirs. Borregos field in Kleberg County, drawing from seventeen reservoirs, is the most prolific. The main and zone fields gave up a cumulative total of more than one trillion cubic feet of gas by 1989 to become the most prolific Vicksburg gas-producing area in Texas.
Because of the wealth of both multi-pay and closed reservoirs in the trend, cooperation among operators and unitization of leases are requirements for maintaining reservoir pressure and for recovering the ultimate volume of hydrocarbons. Oil well-spacing is on forty-acre units and gas well-spacing varies from 40 to 640 acres. Primary recovery in the fields was accomplished by large gas-cap expansion or by a combination of gas-cap and local water drive. Pressure in the diverse reservoirs has been maintained by gas injection, water injection, waterflood, and polymer flood. Infill drilling and recompletion of wells has been employed for enhanced ultimate yields. Collectively, the Vicksburg Fault Zone fields reported a cumulative production that exceeded 917 million barrels of oil by 1981. By 1994 the major areas-main and zone fields-of the trend had given up a cumulative total of nearly 1.12 billion barrels of oil, and from 1970 through 1993 a total of 5.98 trillion cubic feet of gas was reported.
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