Matrix acidizing has been a successful stimulation method to enhance production in carbonate reservoirs. One of the challenges is to distribute the acid evenly along the interest zone to achieve a maximum stimulation effect, due to the differences in porosity, permeability and degree of damage along the interest zone.Well-S delineation gas well, located in Senoro Field Sulawesi-Indonesia, is drilled through a carbonate reservoir. It was decided to use an acid soluble diversion agent instead of conventional proppant. This diversion agent is an acid system that contains a polymer that crosslinks as the acid spends to near completion, with this crosslink then disappearing as the acid spends more completely over time. The non-crosslinked spent acid can then be flowed back from the formation with relative ease.Acid solubility test for 15% HCl and crosslinked acid was performed to design the acid job and the result showed that Senoro carbonate has 90% solubility. This crosslinked acid serves as a diversion agent that will facilitate the acid to be evenly distributed along the interest zone. The well test result before stimulation was 13 MMSCFD gas with skin value of +3 (obtained from PBU test), while permeability was 4 md. The well was tested again after stimulation. Significant increased gas rate was observed while the skin damage decreased. This paper describes the planning and implementation of crosslinked acid application as an effective diversion agent in long interval matrix acidizing stimulation. Furthermore, it explains the criteria to determine the efficiency of this application.

Most of oil and gas wells in Indonesia are developed in Sumatra and Java. Central Sulawesi is one area in Indonesia that previously didn't really have high activity in oil and gas because of its location that drives the logistics to become an issue. Central Sulawesi now is showing more activities on oil and gas exploration and production with the presence of Tiaka field that produced about 2,981 BOPD (Dec-07). This paper covers several stimulation works performed in Tiaka field, Central Sulawesi. The produced oil is being temporaryly stored in an FSO facility and then transported to refinery in Indonesia or exported.Tiaka wells are drilled at some angles into Tomori formation, a thick carbonate formation which ranges from 70' -131' in thickness containing 28 API oil. Porosity varies from 10% -15%. Four wells (Tiaka #5, 6, 7, 8) were completed with cemented casing and perforated across the target zone. Two wells (Tiaka #9, 10) were completed with uncemented preperforated liner across the target zone. Length of perforation for stimulation work ranges from 170' -840'.Combinations of hydrochloric acid and acetic acid were used and the composition was held constant for all acid stimulated Tiaka wells. However several acid volume loadings (in gal per ft of interval treated) were tried to optimize the treatment. Several acid placement methods were tried: high rate acid treatment with gelled acid and acid through CT.All stimulated wells showed significant production increase compared to their production rates prior to stimulation. Discussion is made on which methods gives the best production result for the existing wells and the preferred method of stimulation for the future Tiaka development wells. This paper details the application of acid stimulation works in 5 Tiaka wells, post treatment well performance, best practices, and lessons learned.

Well testing generates essential reservoir data, and although it can impact initial operating expenditures significantly in oil or gas upstream projects, the data generated can be essential to the efficiency of the completion operation ultimately designed. While having proven its value, data-gathering methods still must be balanced with operational and economic strategies, if the completion goals are to be economically feasible. Drill-Stem Test (DST) tools with downhole shut in and memory gauges are commonly used in well testing operations to provide reliable data and enhance operational efficiency of the completion. However, DST tools alone cannot monitor reservoir pressure response in real-time for justifying the subsequent operational objective changes during the data acquisition, because the recorded data cannot be retrieved at surface until the well test operation is completed, and the workstring is pulled out of hole. To overcome this problem, surface read-out (SRO) systems can be used with DST for retrieving downhole memory-gauge data in real time; thus, the pressure response can be monitored directly, and operational changes can be made immediately, based on actual reservoir conditions. An SRO system was used in Senoro-6 well to aid in justifying a shut-in duration to reach reservoir boundary and attain information that indicated the need for a stimulation treatment. Based on the real-time SRO data, it was found out that the permeability was lower than expected, and shut-in should be terminated earlier than planned, since the required shut-in time to reach boundary would be much longer than anticipated. Prolonging testing time would not be reasonable when reviewing operational and economic considerations. In addition, pressure transient analysis from real time SRO data indicated that the well had severe wellbore damage. Thus, the decision was made to conduct matrix acid stimulation based on the SRO data and to continue with post-stimulation well testing without pulling the DST string out of the hole. Post-test results showed a 22% production improvement, while the operation itself saved more than US$150,000 from daily rig cost. This approach in using the SRO system proved to be effective in helping to determine an efficient testing operation and completion strategy.