Preserving Great Discoveries by Using Non-Damaging Killing Fluid During the Temporary Abandonment of HPHT Exploratory Wells

Abstract

Objective of this paper is to present the successful method applied to eliminate the damage caused by mud invasion during killing operation after successful testing of newly discovered reservoirs using Drill Stim Test (DST) and before running the completion. DST is normally used during testing the exploratory wells to record the downhole pressure and temperature and to collect downhole samples. After a successful well testing and proving the hydrocarbon potential, the test is called off and the well is usually killed with mud in order to retrieve the DST and run the completion. Heavy oil based mud (OBM) is normally used during killing HPHT wells, which causes severe damage to the treated/stimulated zone. After running the completion, the well is activated by displacing the killing mud with diesel using coiled tubing (CT). In most cases, the wells showed lower productivity after the completion due to the damage caused by mud invasion and barite settlement. In order to overcome this serious issue, non-damaging killing fluid with Calcium Carbonate (CaCO3) pill was used in several exploratory wells. The pill causes a temporary barrier between the perforated intervals and the killing fluid (OBM) to prevent the mud invasion to the discovered reservoir. The CaCo3 pill is an acid soluble material, which can be easily dissolved with Hydrochloric acid (HCl). After killing the well using OBM with CaCO3 pill, retrieving the DST and running the completion, the well is normally activated by displacing the killing fluid with diesel then spotting and squeezing 15% HCl against the perforated intervals. Finally, the well is flowed back for cleaning and flow measurement to confirm that the discovered reservoir is preserved. Excessive Losses of mud into the stimulated/discovered reservoir has always been a major concern during well completion operations since it leads to massive formation damage, which is difficult to be stimulated. Successful implementation of this method using CaCO3 pill in HPHT discovered reservoir has eliminated the mud invasion into the treated zone. During killing process, it was observed that the mud losses were significantly reduced by using fine to medium grains of CaCO3 in the pill. The flow back after acid wash has clearly showed similar productivity to the initial testing results prior killing. Many discovered wells were successfully preserved after treating them with small quantity of acid wash. Field application of this method in more than 10 deep HPHT exploratory wells has preserved them for future production. Using the non-damaging killing fluid with CaCO3 pill for the future exploratory wells, where the DST is mandatory, will eliminate any formation damage to the discovered reservoirs with good hydrocarbon potential which will preserve the well productivity after running the completion.