Corpus Christi Bay—Another 3D Success
Robert M. Rice
Royal Exploration Co., Inc., 500 N. Shoreline Blvd., Ste. 807, Corpus Christi, Texas 78471
Sabco Oil & Gas Corp. and Royal Oil & Gas Corp. formed a partnership in 1997 to exploit state leases in Corpus Christi Bay held by production by Sabco with the remnants of excellent Frio production discovered between 1952 and 1970. The partnership was consummated on the day that 80 square miles of Western Geophysical speculative 3D in western Corpus Christi Bay was released. The partnership concentrated on two fields, East Corpus Christi and Encinal Channel, which are downthrown to a large growth fault which extends across the midsection of the bay. The two fields are located on a shale cored ridge which is perpendicular to the growth fault. East Corpus Christi Field is closest to the fault and had produced 90 billion cubic feet (BCF) from Upper Frio sands aged from Marginulina (-6000 ft subsea) through Nonion struma (-9000 ft subsea. The field is non-geopressured and structurally simple. The sands are massive with short (20-50 ft) shale intervals and thus, with the exception of the Marginulina, the trapping mechanism is anticlinal closure. Encinal Channel Field is southeast of East Corpus Christi Field and becomes the dominant structural feature with depth, starting at -9000 ft subsea at the base of the Upper Frio Nonion struma section and producing down to the Middle Frio Discorbis “D” at -12,500 ft subsea. The field produced in excess of 150 BCF with most of the sands being geopressured and the faulting becoming increasingly complex with depth. The sands vary from 20-150 ft gross thickness with the shale intervals being much more abundant and thicker than at East Corpus Christi Field. The thicker shales are what make upthrown fault closures seal and when combined with a complex fault pattern offer an ideal 3D candidate. The entire two field complex had been discovered and exploited prior to the advent of high quality 2D data, leaving a prospect with major league reserves and no modern seismic data. Encinal Channel also had a key clue well, the Gulf State Tract 48 #2, which had produced 2.6 BCF of gas prior to watering out from the Middle Frio M-4 sand at -10,586 ft subsea. The well had a water contact and by subsurface control was known to be 300 ft low to the top of the structure. There appeared to be 700 acres of unproduced prospective area between the 48 #2 and the next highest producing well. The 3D interpretation confirmed the existence of several fault blocks in the 700 acre target area. The Sabco/Royal partnership drilled these fault blocks first and along with other 3D identified fault blocks, eventually drilling 17 successful wells and 3 dry holes which resulted in peak production of 60 million cubic feet per day (MMCFD) and additional production to date of approximately 40 BCF and 800,000 barrels of oil. In early 2007, the production was still 20 MMCFD. Thus, Corpus Christi Bay was brought back to life and can be added to the long list of 3D success stories.
AAPG Search and Discover Article #90069©2007 GCAGS 57th Annual Convention, Corpus Christi, Texas