TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractWith the realization that water injection is generally taking place under fracturing conditions, tools capable of better modelling fractured injection and its impact are being developed. Models integrating rock (fracture) mechanics and traditional reservoir simulation are now applied to water injection projects with a number of applications in the Middle East. Fracture dimensions are a key input to those models. Monitoring techniques to track the evolution of induced fractures with time are also being deployed. Amongst those techniques microseismic and specific fall-off test procedures are used.
Novel modelling technologies that includes induced fractures in a dynamic reservoir simulator has been used to analyse subsurface aspects of an inverted 5-spot injection pilot. The techniques have allowed an accurate depiction of growing induced fractures. Simulation results indicate that induced fracture growth is limited at injection rates < 200 m3/d but that higher injection rates will result in fracture propagation and a risk of rapid water breakthrough. The results have been validated by field observations. A controlled and cautious increase in injection rate has resulted in a positive production response with rate increases of 50–100% in three of the four producers in the pilot. Results from the pilot have increased the current reservoir understanding and reduced subsurface uncertainties. The knowledge gained is being included in an updated Field Development Plan that will be issued in 2005. The plan will incorporate an optimised injection strategy by a careful and controlled ramp up in injection rate. This project has also advanced induced fracture research with a field verification of the predictive capabilities of the modelling technology. Introduction The Marmul Haima West sandstone reservoir in South Oman, containing heavy and viscous crude (22 ºAPI, μo = 90 cP) and on production since 1980, was initially developed on depletion/solution gas drive using vertical wells. To boost production and improve recovery, an aggressive waterflood development using horizontal wells was initiated in 1999. The development was, however, stopped prematurely in 2000 after excessive induced fracture growth resulted in water short-circuiting and poor well performances. To improve subsurface understanding and redefine a development strategy, an inverted 5-spot produced water injection pilot project was initiated in 2002 with the procurement and construction of dedicated water cleaning and injection facilities and drilling of 5 new vertical pilot wells (i.e. wells I-1, P-1, P-2, P-3 and P-4). A map of the field and the placement of the 5-spot pilot have been shown in Figure 1.
Proposal Numerous oil-producing wells in Southern Oman are completed with wire wrap screens (WWS), internal gravel packs (IGPs), and predrilled liners. These wells produce from mature clastic formations where fines migration and subsequent blockage of screens can result in impaired oil production. In the past, conventional treatment using coiled tubing and a jetting tool has been chosen to remove this damage. The gains resulting from these intervention activities were more often than not short-lived. This lack of longevity required frequent well intervention and oil deferment, often resulting in a loss of revenue. Recently, a systematic approach was undertaken to evaluate the wellbore cleaning and stimulation tools that are currently available in the industry. This approach was implemented as a trial of three cleanout tools in oil-producing wells. This paper describes the results of using these tools for cleanout and stimulation of sand screens. Excellent success was achieved with a pulse-jetting tool operating on the Principles of Coanda effect. This tool is further described in the following sections, and results of its use in a number of oil-producing wells are presented. The effect of the cleanout procedure is presented in terms of initial production and sustainment of production level. This paper also outlines the importance of using proper cleaning and/or stimulation fluid. To help avoid clay-swelling problems, special emphasis is placed on the brine fluid salt concentration. Based on the success it has achieved, the pulse-jetting tool is now a standard tool used in well interventions geared for wellbore cleanout and/or stimulation. The versatility of the tool enables it to be deployed for use with coiled tubing or regular workover strings. Many fluids, including nitrogen, can be pumped through the tool. This versatility is important because most of the wells are sub-hydrostatic and require the use of nitrified fluid to maintain circulation in case cleanout and well-lifting operations occur immediately after sandstone acid stimulation. Introduction Screens are installed in wells to prevent formation sand from being produced along with the oil. These screens, however, are prone to plugging, which in turn leads to reduced production. This problem is currently solved by bullheading brine into the annulus, which flushes the sand off the screen face when coiled tubing units are not available. Although this treatment is cheap in restoring some of the productivity, it is ineffective with short-lived gains, very localized, and needs to be repeated every three months. Frequent application of bullhead treatments can increase the risk of formation impairment and associated reduction in production. To help avoid these problems, three cleaning tools from different service companies were used and evaluated: a rotational-cavitation jetting tool from Service Company A, a piezo-electric sonic tool (PST) from Service Company B, and a pulse-jetting tool from Service Company C. Results of the Trials Rotational-Cavitation Tool Trial runs of the tool were completed in 2001. Nine jobs were performed. In general, the initial cleanup of WWS generated oil gain and raised the fluid level for the wells. The increased production level was not sustained for more than one month in some cases, and after three months, all the wells had dropped in gross production. Piezo-Electric Sonic Tool Trial runs of the PST acoustic tool were completed in October 2002. Five jobs were performed. In general, the initial cleanups of gravel pack (GP) WWS generated oil gain and raised the fluid level for the wells (gross increased). The increased production level in three of the wells was not sustained for more than one month, and in the other two cases, no improvement in production was observed.
The Champion West (CW) field Offshore Brunei, North Borneo consists of alarge number of vertically stacked hydrocarbon bearing reservoirs where thinlayers of laterally continuous shales are sealing the different hydrocarboncolumns. Wells in CW are typically completed selectively on multiple reservoirs (3–5zones) due to contrasting reservoir pressures and fluid properties and forreservoir management purposes. Although the reservoir rock is relativelyconsolidated, sand exclusion has been installed on shallower reservoirsfollowing sand failure in offset wells. Internal Gravel Packing (IGP) has inthe past been the preferred sand exclusion technique. Due to a high deviation in the four CW Early Oil Development (EOD) wells(54–66 deg.), it was desired to incorporate remote operated smart wellequipment to minimise future well intervention requirements. As the large distance between zones would require up to four IGP operationsper well (resulting in high costs) and would not provide sufficientthrough-bore to install the smart well equipment, it was decided to useExpandable Sand Screens (ESS) for sand control purposes in the new wells. Theuse of ESS facilitates multiple zones to be completed in single installationswhilst providing a larger through-bore for the installation of smart wellequipment. The paper discusses the sand-face completion design and installationaspects. As one of the EOD wells was completed with IGP, a benchmarking (rigtime, cost, performance) of the ESS technique is also presented. Finally, recommendations are made which should enable further cost reductions in thefuture. Introduction Champion West is situated 7 km N-NW of the Champion Main field offshoreBrunei. The field was discovered and put on production in 1975. By end 2000, some 16 wells have been drilled of which 10 are producers. An appraisal welldrilled in 1997 proved up new oil volumes and based on the results, an EarlyOil Development drilling campaign, consisting of four wells (CW-12/13/14/15), was executed during January - June 2000 to target undeveloped reserves andappraise new reservoirs. Operational Summary The CW EOD wells were drilled and completed in batch mode from splitterwellheads on an offshore well jacket. Drilling and completion details arepresented in Table 1. Each well was perforated on 3–5 zones using 4.5" TCPHSD guns under 5000 kPa drawdown. Big hole (RDX charges, 12 spf) were usedwhere sand control (ESS or IGP) was required to maximise the area open to flow.Sand control was installed and the wells were completed as single selectivemulti-zone producers using smart well technology (mini-hydraulic inflow controlvalves and permanent gauges) for reservoir management purposes and to minimisefuture well intervention requirements.
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