Use of Inverted-Emulsion Mud Proves Successful in Zones Susceptible to Water Damage

Abstract

Abstract Extreme difficulties in well completions in Pennsylvanian age sands in Central Oklahoma led to the use of an inverted-emulsion mud for drilling-in, completion and workover operations in this area. This mud, containing about equal volumes of oil and water or water-base mud and emulsified by a modified wood product, has been employed successfully in over 150 operations over a six-year period. In zones that are susceptible to water damage, improved formation evaluation, better well completions and effective recompletion of damaged wells have been achieved. Mud is stored and re-used extensively. Testing and maintenance are relatively simple and inexpensive. The geological interpretation of formations has been adequate where the hole has been drilled with this mud. The mud offers no advantage in limestone or dolomite completion, and it may slow drilling rates in shale. Early Well Completion Experience In Central Oklahoma the majority of wells are in and the greater part of oil production is from sands of Pennsylvanian age. A number of formations are represented, of which the Springer and Hart sands are two of the better known. Prior to 1953, the Mobil Oil Co. (then Magnolia Petroleum Co.) experienced severe difficulties in many well completions in various of these sands. Other operators in this area were having similar difficulties. A characteristic experience follows. Drilling with a water-base mud (as was customary in this area), a well penetrated one or more Pennsylvanian age sands. At the time of penetration, drill-stem tests indicated fair producing rates. When completion of the well was attempted after further exposure of the sand to drilling mud or water, production was often much lower than indicated by the drill-stem test. In some extreme cases, no production could be obtained. In an outstanding example, oil flowed at 30 bbl per hour on drill-stem test, but could not be made to produce afterwards. Well stimulation techniques, including acidizing and fracturing, were not effective in obtaining satisfactory completions. In some cases, attempted stimulation procedures, as employed, caused further decreases in production of oil.