Granite Point field is located 50 miles southwest of Anchorage. A redevelopment program on the southernmost platform included two high-angle single zone wells. Use of computer-modeled responses in conjunction with 2 MHz resistivity technology assisted in placing the two wellbores accurately in the reservoir.
Granite Point field in Cook Inlet, Alaska, (Figure 1), was discovered in 1965. Platforms were set in 1967, and most primary development drilling was completed by the mid '70s. In 1992, Unocal embarked on a redevelopment program on the southernmost of the three platforms.
The Granite Point structure is an asymmetric anticline, about 7 miles long by 1 1/2 miles wide. (Figure 2) The steep, faulted west flank dips at about 70 degrees, while the east flank dips at between 18 and 22 degrees. Production comes chiefly from the lower Tyonek Formation, of Oligo-Miocene age.
It consists of braided fluvial conglomeratic sands, with interbedded silts and coals. The average porosity is 11 - 13 %, and the average permeability, about 35 md. Recently production was established from the underlying Hemlock Formation, an Eocene-Oligocene fanglomerate, and the principal producer in most other fields in Cook Inlet.
A redevelopment program was begun in 1992 from the Granite Point Platform, in conjunction with partner Mobil. Two wells were drilled to the Hemlock, and two single zone producers were completed in the Tyonek. (Figure 3) This paper discusses the two Tyonek wells. A consideration in planning these wells was the fact that structural control was such that mud logging and MWD were needed to detect bed boundaries. As these boundaries were detected, drilling personnel were advised to maintain the well path.
Modeling of anticipated responses of MWD resistivities was done beforehand, using offsetting well data, to aid in interpreting actual data as it was received. Thus, a model-derived resistivity log was provided to compare with real-time log data.