The accurate placement of directionally controlled wellbores is essential in order to maximize oil production while avoiding collisions with existing wells. Error models provide estimates of the positional uncertainty that can be expected when using a specific survey tool. For example, a Measurement While Drilling (MWD) tool will have a different ellipsoid of uncertainty when compared to a Gyro While Drilling (GWD) or a continuous gyro tool. Whichever survey tool is chosen, the uncertainty in the calculated wellbore position is dependent on the trajectory and latitude of the planned wellbore. Many drilling projects have been designed assuming specific survey instruments and favorable drilling directions. However, these assumptions are often not fulfilled due to existing wellbores, environmental safety concerns, land management issues, drilling costs and survey tools available. Different azimuthal corrections and methods of surveying have been deployed to increase confidence in the wellbore placement when drilling wells in east or west directions at high inclinations. MWD surveys with magnetic interference corrections and rate-gyro surveying on wireline are two examples of these methods. Previous GWD technology was limited to 70 degrees of inclination and was not an option for high angle and horizontal wells. With the development of an all-attitude GWD tool, it is now possible to provide accurate gyroscopic surveys at all inclinations and all directions during the drilling process in real time.
This paper describes a case study in which the all-attitude GWD tool was utilized to achieve tighter control of well trajectories drilled predominantly in an easterly direction in close proximity to a number of existing wellbores. This approach allowed a significant reduction in costs since it became possible to drill all the wells from an existing pad and so avoid land management and environmental concerns initially associated with the project. Further, the accuracy of an all-attitude GWD tool allowed the operator to drill safely through an additional 1,000 feet of geological pay zone, a result that could not have been achieved safely using MWD surveys alone.
Willhite, G. Paul (Universityof Kansas) | Byrnes, Alan P. (Chesapeake Energy Corp) | Dubois, Martin K. (Improved Hydrocarbon Recovery LLC) | Pancake, Richard E. (Murfin Drilling Company) | Tsau, Jyun-Syung (University of Kansas) | Daniels, James R. (Murfin Drilling Company) | Flanders, William
A pilot carbon dioxide (CO2) -miscible flood was initiated in the Lansing-Kansas City C formation in the Hall-Gurney Field, Russell County, Kansas. The reservoir zone is an oomoldic limestone located at a depth of approximately 2,900 ft. The pilot consisted of one CO2 injection well and three production wells. Continuous CO2 injection began in December 2003 and continued through June 2005, at which point 16.19 million lbm of CO2 had been injected into the pilot area. Injection was converted to water in June 2005 to reduce operating costs to a break-even level with the expectation that sufficient CO2 was injected to displace the oil bank to the production wells by water injection. By March 2010, 8,736 bbl of oil had been produced from the pilot. Production from wells to the northwest of the pilot region indicated that oil displaced by CO2 injection was produced from five wells outside of the pilot area, to the northwest. Approximately 19,166 bbl of incremental oil was estimated to have been produced from these wells as of March 2010. There was evidence of a directional permeability trend toward the northwest through the pilot region. The majority of the injected CO2 remained in the pilot region, which was maintained at or above the minimum miscibility pressure (MMP). Although the four-well pilot was uneconomical, the estimated oil recovery attributed to the CO2 flood is 27,902 bbl, which is equivalent to a gross CO2 usage of 4.8 Mcf/bbl.