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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
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Recent increases in gas price and subsequent drilling activity have resulted in a second look at old developed gas fields with marginal or submarginal production with the hope of improving the economics of gas development through reservoir analysis, drilling and completion methods, and the development of new or "hidden" reserves.
One of the deterrents to selling this type of prospect is the stigma of certain formation names and geographic areas in the mind of a prospective operator, his investor, or the prospect analyst.
Evaluation of oil and gas potential of development areas is enhanced significantly by a "look at the rocks." These studies of basic rock properties through examination of well samples and cores (porosity, permeability, grain density, pore size and distribution, pore-wall composition, and gas-fluid distribution) along with good electric logs are the dominant ingredients for effective reservoir analysis and completion designs.
With these tools one is equipped to evaluate (1) the significance of the rate of natural flow in air drilling, of drillstem tests in relation to gas or oil in place, (2) inplace reserves from electric logs, (3) economic feasibility for completing or plugging, and (4) completion designs.
Close supervision and planning were required to obtain good samples, test data, and electric logs. Poor electric logs result from rough well-bore conditions. In air-drilled holes "rough hole" and subsequent poor logs commonly are a result of "reducing well cost" by conserving casing through possible water zones. This cost-saving philosophy generally results in lost reserves in areas of low-permeability reservoirs.
Many areas of poor production are the result of cement and perforating problems. These problems can be recognized, avoided, and corrected with safeguard methods.
Development drilling is often complicated by lateral changes in gas-fluid ratios due to structural or stratigraphic separation and fossilized hydrodynamics. These problems are further complicated by inaccurate well elevations and subsequent poor structure maps.
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