The properties of low density foamed cement slurries have been advantageously employed to overcome cementing problems in North and South Dakota, Wyoming, and Montana. For over 30 years, operators in the Williston Basin have encountered completion problems associated with several salt and lost circulation zones. Poor mud displacement in washed out salt sections left long string production casing vulnerable to casing collapse. Weak zones prone to lost circulation necessitated use of multiple stage cementing techniques to perform long string casing cementing jobs. To solve these problems, foam cement has been used with exceptional success. The use of this lightweight cementing system has helped eliminate the problem of collapsed pipe, as well as allowing for the circulation of long intervals of cement, even back to surface, in a single stage.
The industry is faced with the task of producing hydrocarbon from increasingly tighter reservoir rock, including low-permeability sand and shale. As a consequence, the selection of an appropriate well type and fracture-stimulation design is becoming more critical to project success. The purpose of this paper is to provide some clarity by providing a general understanding about the effects of well-type selection and hydraulic-fracture design on hydrocarbon recovery for various reservoir-permeability scenarios. Well types modeled include vertical, stimulated vertical, horizontal, axial-stimulated horizontal, and transverse stimulated horizontal with variations in compartment length and effective fracture length. This information has proven useful in the evaluation and planning of moderate to low to ultralow-permeability well projects. The summaries presented in this paper are a compilation of the results from numerous simulator runs for black oil, gas condensate, and gas cases. These simulator runs included sensitivities on well type and permeability to compare recovery and production. Important conclusions pertaining to the recovery of hydrocarbon from low-permeability reservoirs and shale are made. In addition to validating the obvious conclusion about the increasing difficulty in recovering hydrocarbons from lower-permeability rock, a primary conclusion is that, as reservoir permeability decreases, proper well-type selection and correct hydraulic-fracture-stimulation design becomes much more crucial. The conclusions also show that, for a given permeability, obtaining significant recovery of oil can be a much more difficult problem than with dry gas.
The industry is faced with the task of producing hydrocarbons from increasingly tighter reservoir rock including ultra low permeability sand and shale. As a consequence, the selection of an appropriate well type and fracture stimulation design is becoming even more critical to project success. The purpose of this paper is to provide some clarity by providing a general understanding about the effects of well type selection and hydraulic fracturing on hydrocarbon recovery for various reservoir permeability scenarios. Well types modeled include vertical, stimulated vertical, horizontal, axial stimulated horizontal and transverse stimulated horizontal with variations in compartment length and effective fracture length. This information has proven useful in the evaluation and planning of moderate to low to ultra low permeability well projects. The summaries that will be presented in this paper are a compilation of the results from numerous simulator runs for gas, black oil and gas condensate cases. These simulator runs included sensitivities on well type and permeability in order to compare recovery and production. Important conclusions pertaining to the recovery of hydrocarbons from ultra low permeability reservoirs and shale are made. In addition the obvious conclusion about the increasing difficulty of recovering hydrocarbons from lower permeability rock, a primary conclusion is that as reservoir permeability decreases, proper well type selection and effective hydraulic fracture stimulation design become much more crucial. The conclusions also show that for a given permeability, obtaining significant recovery of oil can be a much more difficult problem than with that of dry gas. These conclusions are supported by Bakken and Barnett Shale case histories which are included in this publication.
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