No abstract

In Central Graben, North Sea, there is generally no free water production, most of the produced water is condensed water; however wells have been treated against scale build up at perforation level by performing acid washes using mainly acetic acid. Wells reacted differently after acid treatment: Some wells showed a significant productivity improvement, others showed good results but limited in time, some wells presented no gain after acid treatment and some other wells are scaling on a more aggressive basis after acidification. This paper shows that these behaviours are linked with the lithology of the different reservoirs. A better understanding on the scale formation and mechanism is essential in order to optimize the well intervention planning and timing to treat the wells. This study showed that calcium carbonate and sodium chloride are the only scale deposits susceptible to precipitate at the bottomholes of wells. The precipitation of sodium chloride has been induced by the high salinity of water associated with a high temperature at bottomholes as well as an inversion of the Joule-Thomson coefficient. Calculations showed that evaporation is slightly higher for Elgin reservoirs comparing to Franklin reservoirs, this is due to Joule-Thomson effect slightly stronger and a higher temperature reservoir for Elgin reservoirs. These high temperatures at the bottomholes induced the formation of calcium carbonate precipitation, this conducted to the loss of productivity. From the subsurface safety valve (SCSSV) to the surface facilities, the reduction of temperature caused a reduction of solubility of zinc sulphide and lead sulphide. In terms of chronology, halite scale occurred first, followed by carbonate scale and finally formation of sulphide scale at lower temperature.

The Delta Mahakam's geology is characterized by multiple layers of thin, heterogeneous reservoirs separated by a few meters. These wells are traditionally perforated with the conventional wireline method. However, at reservoir porosities less than 11%, perforations yielded less than 60% of flowing probability. With the increase in drilling activity and the number of reservoirs with low porosities, we began to evaluate the effectiveness of perforating these reservoirs with abrasive jets perforation conveyed on coiled tubing (CT).To improve depth accuracy and monitor real-time bottomhole conditions, the abrasive jet perforating tool was run on fiber-optic CT. Pressure measurements inside and outside the coiled tubing enabled the pumping rate of the abrasive fluid to be adjusted as necessary, improving perforating efficiency as well as the GR/CCL reading for the depth correlation.This abrasive perforation method was applied in six different wells in Delta Mahakam field; the design, execution, and evaluation of this method is presented. From the first well to the last, this alternative perforating strategy helped increase reservoir production, improve cost efficiency, and by adding the real time monitoring system on coiled tubing it is proved of reducing the operational time by up to 45%. This method proved to be a viable alternative to wireline-conveyed perforating in the Delta Mahakam field.

In unconsolidated sand reservoirs, proper sand control completion methods are necessary to help prevent reservoir sand production. Failure due to sand production from surface equipment damage to downhole equipment failures which can ultimately result in loss of well integrity and worst-case catastrophic failure. Gravel Packing is currently the most widely used sand control method for controlling sand production in the oil and gas industry to deliver a proppant filter in the annular space between an unconsolidated formation and a centralized integrated screen in front of target zones. Additional mechanical skin and proper proppant packing downhole are the most critical objective when implementing gravel packs as part of a completion operation. This paper presents a case history of Well SX that was designed as single-trip multi-zone completion 7-inch casing, S-shape well type, having 86 deg inclination along 1300 meters, 4 to 5-meter perforation range interval and 54 deg inclination in front of the reservoir with total depth of 3800 mMD. The well consists of 4 zones of interest which had previously been treated with a two-trip gravel pack system. While Well NX was designed as single-trip multi-zone completion in 7-inch casing, J-shape well type, 8-meter perforation interval and 84 deg inclination in front of the reservoir with total depth of 3300 mMD. The well consists of two zones of interest which had previously been treated with a single-trip gravel pack system. Both wells are in the Sisi-Nubi field offshore Mahakam on East Kalimantan Province of Borneo, Indonesia. This paper discusses the downhole completion design and operation as well as the changes to the gravel pack carrier which overcame challenges such as high friction in the 7" lower completion and the potential for an improper annular gravel pack due to the lack of shunt tubes in a highly deviated wellbore. In vertical wellbores, obtaining a complete annular pack is relatively easy to accomplish but in highly deviated wellbores, the annular gravel pack is more difficult to achieve and can contribute additional skin. Tibbles at al (2007) noted that installing a conventional gravel pack could result in skin values of 40 to 50, mostly due to poor proppant packing in perforation tunnels. Therefore, operator required to find a reliable gravel pack carrier fluid optimization for typical highly deviated wells to overcome the potential sand production issues by applying a single-trip multi-zone sand control system across both zones (without shunt tubes) along with the utilization of a high-grade xanthan biopolymer gravel pack carrier fluid. Laboratory testing was conducted to ensure that the gravel pack fluid could transport the sand to the sand control completion, large enough to allow for a complete annular pack and still allow the excess slurry to be circulated out of the hole. Electronic gravel pack simulations were performed to ensure that rate/pressure/sand concentration would allow for a complete gravel pack. All four zones in Both of Well SX and NX were successfully gravel packed with a high rate, relatively high sand concentration slurry. The well has not exhibited any sand production issues to date. The current production from both wells is above expectation and are comingled from the two primary zones. Multiple factors were considered during the design and operation of the sand control treatment. Those factors will be described in this paper, starting with candidate selection, completion strategy, operational challenges and treatment execution along with production monitoring of the well.

In Central Graben, North Sea, there is generally no free water production, most of the produced water is condensed water; however wells have been treated against scale build up at perforation level by performing acid washes using mainly acetic acid. Wells reacted differently after acid treatment: Some wells showed a significant productivity improvement, others showed good results but limited in time, some wells presented no gain after acid treatment and some other wells are scaling on a more aggressive basis after acidification. This paper shows that these behaviours are linked with the lithology of the different reservoirs. A better understanding on the scale formation and mechanism is essential in order to optimize the well intervention planning and timing to treat the wells. This study showed that calcium carbonate and sodium chloride are the only scale deposits susceptible to precipitate at the bottomholes of wells. The precipitation of sodium chloride has been induced by the high salinity of water associated with a high temperature at bottomholes as well as an inversion of the Joule- Thomson coefficient. Calculations showed that evaporation is slightly higher for Elgin reservoirs comparing to Franklin reservoirs, this is due to Joule-Thomson effect slightly stronger and a higher temperature reservoir for Elgin reservoirs. These high temperatures at the bottomholes induced the formation of calcium carbonate precipitation, this conducted to the loss of productivity. From the subsurface safety valve (SCSSV) to the surface facilities, the reduction of temperature caused a reduction of solubility of zinc sulphide and lead sulphide. In terms of chronology, halite scale occurred first, followed by carbonate scale and finally formation of sulphide scale at lower temperature.