Preformed Stable Foam Performance in Drilling And Evaluating Shallow Gas Wells in Alberta

Abstract

Conventional drilling and evaluation of shallow gas wells producing from low-pressure, fractured, vuggy reef formations was expensive and provided inconclusive results. Introducing preformed stable foam as a circulating fluid for drilling and coring the productive reef section of the hole proved inexpensive, fast, effective, and not damaging to the formation. proved inexpensive, fast, effective, and not damaging to the formation. Introduction Development and exploratory drilling in the Calling Lake-Algar area of northeastern Alberta involves penetration and evaluation of a shallow, low-pressure, vuggy, and fractured reef. Original procedures used conventional mud and/or water to drill this procedures used conventional mud and/or water to drill this formation. Because of the large volume of fluid lost to the formation, inconclusive drillstem-test (DST) and log-evaluation results were obtained. In addition, a stimulation treatment and a lengthy cleanup program were required to obtain diagnostic evaluation results. Following the introduction of preformed stable foam as a drilling fluid, a continuous evaluation of the formation was obtained during drilling. History of the Program The original wells, House River 11-19-82-15 W4 and Grand Rapids 11-25-83-14 W4, experienced severe circulation-material loss in the objective formation porosity. Large volumes of drilling mud and circulation material were lost to the formation, resulting in mud bills of $2,800 and $10,500, respectively. Since then, mud costs have been reduced to about $800/well by using mud only on the upper hole. Because of the low reservoir pressure (200 psi at 1,000 ft), low-volume reservoir-fluid output, and flushing of the zone by mud and lost circulation material, no definitive results were obtained by drillstem testing. Seven misruns occurred in the House River and Grand Rapids wells (mostly because of tool plugging) at a cost of $13,200 (rig cost not included). About 5 rig days were used in these attempts. No reservoir fluid was recovered during any of the DST's. As a result, the Grand Rapids well was abandoned and the House River well was completed on log analysis only. Following removal of drilling equipment from the House River 11-19-82-15 well, an attempt was made to prove the presence of gas. This involved blowing the well clean with nitrogen 15 times, swabbing for 4 days, and acidizing with 1,000 gal of 15-percent HC1 to clean up the well sufficiently for a flow test. Over-all cost of this cleanup operation was about $30,000. Dubious results obtained about these two wells prompted investigation of the use of a drilling fluid that would permit underbalanced drilling through the carbonate interval. The goals were to (1) reduce over-all expenditures, (2) prevent formation damage and flushing by foreign fluids, and (3) evaluate the wells for possible gas and/or water influx as the formation was penetrated. penetrated. The only drilling fluids available that would give an underbalanced hydrostatic pressure in these wells were straight air or an air-lightened column. Preformed stable foam was selected in preference to straight air because of its greater capacity for preference to straight air because of its greater capacity for carrying cuttings and for its safety aspect in preventing a down-hole explosion and fire. It also gave promise for cleaning out heavy oil residue present in the formation. P. 1237