Targeted Horizontal Well Applications in a Heterogeneous Waterflood Unit: Vacuum Glorieta West Unit, Vacuum Field, Lea County, SE New Mexico

Ata Sagnak, Garrett Luig, Greg Hinterlong
CHEVRONTEXACO, Midland, TX

The Vacuum field is located in the Northwestern Shelf of the Permian Basin in Lea County, New Mexico. Vacuum Glorieta West Unit (VGWU) is one of the two Glorieta units in the field and is located on the western edge of the Vacuum structure. The initial discovery in the Vacuum field was in 1929 in the San Andres formation. The Vacuum Glorieta Pool was discovered in 1963 and was initially developed on 40-acre spacing. The field was divided into two separate waterflood units, Vacuum Glorieta West Unit (VGWU) and Vacuum Glorieta East Unit (VGEU) in 1991. Waterflooding in the VGWU was started in 1992 after the completion of injectors forming a 5-spot pattern. In 1997 the first horizontal well was drilled as a horizontal recompletion.

The VGWU is actually comprised of Glorieta and Paddock formations. The Leonardian Glorieta and Paddock formations are shallow water platform carbonates which were deposited on broad shelf and lagoon environments and occur on the Central Basin Platform, northwestern shelf, and eastern shelf regions of the Permian Basin. The overlying and underlying strata are the Guadalupian San Andres and the Leonardian Clearfork formations respectively. Glorieta and Paddock formations in the Vacuum field consist of alternating layers of shallowing upward cycles, mostly capped with tidal flat and subtidal facies. Subtidal cycles range in lithology from mud-rich to grain-rich rocks and are typically the reservoir intervals especially if capped with subtidal facies.

Despite the original designation as a Glorieta Pool, historically within the unit, the main producing interval has been the Paddock formation. It comprises the lower part of the unitized interval and is subdivided into Upper Paddock and Lower Paddock. Lower Paddock is a fractured dolomite reservoir with good primary production followed by a quick water breakthrough. Upper Paddock in the VGWU area is an oolitic, oolitic-peloidal, fine-to-coarse grained grainstone and packstone. In the southern part of the VGWU, the Upper Paddock is limestone with oolite grainstone shoal developments. The main production in the unit has been from these limestone shoals. To the north, Upper Paddock is extensively dolomitized. Glorieta is the uppermost formation within the unit and is composed of alternating layers of sand/silt, silty dolomite and dolomite beds with thickness range from 2 to 10 ft. Producible porosity is limited to the dolomite beds. Tidal flat capped cycles are common in the Glorieta interval.

Due to its heterogeneous nature, traditionally the Glorieta interval in VGWU has not been the target for waterflooding and horizontal development. Sinusoidal wellbores and geo-steering during drilling operations were deemed not useful because of the heterogeneity and thin bed thicknesses in the Glorieta interval. A new approach in developing the Glorieta interval was implemented in 2003 utilizing medium curvature targeted horizontal wellbores. The structure was modeled in detail and the horizontal re-entries were planned according to the gridded surfaces following single reservoir bed. The horizontal paths were designed to follow the structure, staying in target beds, 5-7 ft in thickness at a total vertical depth of ~ 5900 ft. The horizontal wellbore lengths ranged between 2000 ft and 2400 ft. In 2003, five horizontal re-entries were completed with another one scheduled later in the year. Except one, the average initial rates were 200 BOPD, 150 BWPD, 75 MCFD. The initial high oil and low water rates plus relative low cost in drilling horizontal re-entries makes the Glorieta interval in VGWU an attractive development target. Currently detailed core analysis is being conducted in an effort to better characterize and develop the Glorieta interval.