TX 75083-3836 U.S.A., fax 01-972-952-9435. AbstractDrilling the 12 1/4" sections for the Kharyaga oilfield in the Timan-Pechora region of Russia has always been considerably complicated by wellbore instability and hole cleaning issues. These issues have been most serious when drilling through Triassic and Permian shales, sandstones, argillites and silts, followed by drilling Carboniferous limestones and dolomites. Unstable formations sloughing and packing off, wash outs and severe caving has resulted in many problems including drill pipe pack-offs, high torque and drag, the need for additional reaming operations, and difficulties in reaching bottom with casing.Fluid treatments of swelling shales with chemical inhibitors helped considerably with shales hydration, but the problem of caving and packing off still persisted. High angles (up to 52.8°) and long section lengths (up to 2,707 m) aggravated the problems. The key remedy was determined to be effective hole cleaning. Cleaning efficiency of different types of sweeps was studied during drilling of 10 Kharyaga wells. Sweeps were pumped on a regular basis in drilling intervals of 100, 150, 200 and 300 meters, prior to pulling out of hole and when indications of packing off had been observed.Pumped cleaning sweeps included high-viscosity or highdensity single sweeps; tandem sweeps (low-viscosity following by high-viscosity or high-density sweeps); and sweeps with special additives (carbon-based LCM material or innovative monofilament fiber sweeping agent). Also, special attention was given to combined tandem sweeps, which are low-viscosity sweeps treated with a monofilament fiber sweeping agent followed by a high-density sweep (sometimes treated with carbon-based LCM material).Investigation of different sweeps performance showed that the best hole cleaning results for Kharyaga field wells were achieved by circulating combined tandem sweeps, which are low-viscosity sweeps treated with a monofilament fiber sweeping agent followed by a treated or untreated high-density sweep.
TX 75083-3836 U.S.A., fax 01-972-952-9435. AbstractDrilling the 12 1/4" sections for the Kharyaga oilfield in the Timan-Pechora region of Russia has always been considerably complicated by wellbore instability and hole cleaning issues. These issues have been most serious when drilling through Triassic and Permian shales, sandstones, argillites and silts, followed by drilling Carboniferous limestones and dolomites. Unstable formations sloughing and packing off, wash outs and severe caving has resulted in many problems including drill pipe pack-offs, high torque and drag, the need for additional reaming operations, and difficulties in reaching bottom with casing.Fluid treatments of swelling shales with chemical inhibitors helped considerably with shales hydration, but the problem of caving and packing off still persisted. High angles (up to 52.8°) and long section lengths (up to 2,707 m) aggravated the problems. The key remedy was determined to be effective hole cleaning. Cleaning efficiency of different types of sweeps was studied during drilling of 10 Kharyaga wells. Sweeps were pumped on a regular basis in drilling intervals of 100, 150, 200 and 300 meters, prior to pulling out of hole and when indications of packing off had been observed.Pumped cleaning sweeps included high-viscosity or highdensity single sweeps; tandem sweeps (low-viscosity following by high-viscosity or high-density sweeps); and sweeps with special additives (carbon-based LCM material or innovative monofilament fiber sweeping agent). Also, special attention was given to combined tandem sweeps, which are low-viscosity sweeps treated with a monofilament fiber sweeping agent followed by a high-density sweep (sometimes treated with carbon-based LCM material).Investigation of different sweeps performance showed that the best hole cleaning results for Kharyaga field wells were achieved by circulating combined tandem sweeps, which are low-viscosity sweeps treated with a monofilament fiber sweeping agent followed by a treated or untreated high-density sweep.
TX 75083-3836 U.S.A., fax 01-972-952-9435. AbstractThe Kharyaga field is located in Timan-Petchora region of Northern Russia, 60 km North of the Arctic Polar Circle. The field is producing principally from a Devonian age carbonate reservoir, this limestone formation having an average porosity of 8 to 12% and permeabilities ranging from 1 to 200 mD. The wells are completed as cased-hole, with a 7inch liner through the reservoir section. The perforated intervals range from 30 to 80 m in length and the wells were traditionally matrix-acid stimulated following perforation. The wells produced initially unassisted then later on, a work-over campaign was launched in order to equip the well with electrical submersible pumps (ESP).Work-over operations were taken as an opportunity to restimulate lower-performing wells of the field. Several options were considered for this purpose from mechanically-diverted acid squeeze to propped hydraulic-fracturing or acid-fracturing this later option being ultimately selected. However, the rather adverse conditions existing both downhole and at surface rendered such an operation quite challenging. In the first place, the tectonically active nature of this region (West of Ural) led to anticipate significantly high fracturing gradients and difficulties to initiate a fracturing regime. Secondly, the weather conditions, with surface temperatures ranging from +20°C in summer to -50°C in winter and logistical issues necessitated adjustments to the fracturing fluids and job design. Finally other factors such as a high tendency of the Khariaga crude to precipitate wax, the presence of H2S or the flow-back through the ESP called for additional precautions.In this paper we will show that despite these rather adverse conditions successful acid-fracturing treatments can be implemented in this region; we will discuss some of the key parameters that helped base the choice of treatment type and we will describe the lessons learnt during such treatments.In addition, as the data-set available for this acid-fracturing treatment is unusually comprehensive with image logs, production profiles, pre and post-frac thermal logs, bottomhole gauges and extended post-frac decline, an integrated evaluation of the treatment will be proposed.
Drilling water wells on Kharyaga oilfield, Timan-Pechora region of Russia, often resulted into poor water production due to aquifer formation plugging with weighting materials and drilled solids and insufficient filter cake removal. Bentonite-based drilling fluids have been traditionally used for water wells drilling in this area. Bentonite particles invasion into the unconsolidated sand water-bearing horizons is almost impossible to prevent and cure, so in most of the cases actual water production rates achieved proved to be lower than estimated ones. Also, when the wells were put on production considerable sand control related issues often occured. During the drilling phase, when passing through unconsolidated sands, borehole instability problems due to sands washout and hole sloughing have been frequently experienced. In order to avoid considerable formation damage, borehole instability and increase water production, saturated sized salt drilling fluid system has been proposed for two water wells drilling. Saturated sized salt drilling fluid has been formulated by water saturation with sodium chloride salt following by treatments with modified sized salt of appropriate grade and additions of alkalinity, filtration, viscosity and foaming control agents. The system showed very stable properties throughout operations with tight LPLT filtration, good thin and smooth filter cake and perfect rheological characteristics. Drilling and coring operations in sand and clay formations have been performed with no problems, neither several days of stand-by had any influence on wellbore stability. Electric logs have shown perfect in-gauge hole. After the section has been drilled and liner with filter screens has been run to bottom, the filter cake was easily removed by displacing and circulating hole with fresh water to dissolve sized salt particles. When the water wells were put on production, both of them have shown very good production rates in comparison with other water wells drilled in the field and in comparison with estimated production rates for these two wells also. No signs of sand/fines control related issues have been either experienced during more than two years of water production. Introduction To minimize formation damage due to drill-in and completion fluids solids invasion into the production zone as a whole and aquifer formations in particular, drilling fluids bridging particles should satisfy two important criteria:they should be of appropriate size to rapidly develop a thin and tough external filter cake in order to filter out drill solids and polymers from the filtrate entering the formation; andthis filter cake should be easily and fully removable without much additional force applied onto the formation. Rapidly developing external filter cake prevents solid particles suspended in the drilling fluid from invading deeply into the formation, plugging the pores and hence reducing the rock permeability. A good filter cake also helps to support walls of the unstable wellbore and prevent wash out, sloughing and pack off. If this filter cake can be easily removed (dissolved) during completion operations, this gives an additional advantage of cleaning out and opening the pores plugged by the bridging material particles without additional operations required, such as scraping or washing the filter cake away. Formation protection and consolidation by a good, easily removable filter cake during the drilling phase will not only increase the production rates and decrease skins, but will also help to mitigate any sand and fines control related issues in future, when the well is put on production. Background Among the factors which determine formation damage due to pay-zone particles invasion the following major ones can be pointed out:1
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