Considering Wellbore Friction in Planning Horizontal Wells (includes associated papers 28646 and 29095 )

Abstract

Abstract The importance of friction pressure loss within the completed section of horizontal wells, under some reservoir conditions, has been analyzed. The phenomena were studied both analytically and experimentally with sub sequent implementation in a commercially available 3-D,3-phase reservoir simulation model. Based on simulation studies, criteria for the selection of appropriated imensions for horizontal wells under different reservoir conditions are outlined. A field example from the Troll Field offshore Norway where these results were applied during the planning of a horizontal test well, is presented. Introduction The Troll field, located in 300m water depth offshore Norway (Fig. 1), contains 0–26 m thick oil rims sandwiched between a large gas cap and active aquifers. In the westernmost fault block of the field, the Troll WestOil Province, the oil zone is at its thickest; 22–26 m. The oil in place of this province is estimated at 121x10 6 Sm3.The reservoir contains several highly permeable, unconsolidated sands separated by low permeability micaceous sands. Impermeable calcite cemented horizons with imperfectly known spatial disposition and extensions occur within the high permeability sands. The oil production from Troll may be limited by gas coning, resulting in a limited available drawdown for the well. Since the oil rim is only 22–326 m thick, the drawdown can only be in the range of 1.5 to 2 bar in order to avoid the production of free gas-cap gas. The recoverable oil in the Troll West Oil Province is located in high-quality sands with permeabilities ranging from3000 to 10 000 md, so high liquid rates were expected(Fig. 2). With the combination of limited drawdown and high rates, wellbore friction pressure loss was considered to be of importance [1].The subject has been studied analytically by Dikken [1]. However, implementation of the effect of horizontal well friction in simulators with subsequent application for well planning and design purposes has previously not been reported. Horizontal well friction was given due attention during the planning of a 500 m horizontal well in the Troll field. The well was drilled and completed in late1989, and has been on production since January 10th 1990. The cumulative oil production as of early June1990 was 500 000 Sm [2]. Background The Troll field covers an area of 700km2 . The estimated gas and oil in place is 1670x10 9 Sm3 and 615x10 6 Sm3respectively (Fig. 3). Two main north-south bound faults divide the field into three provinces: Troll West Oil Province, Troll West Gas Province and Troll East(Fig. 3).Concession Block 31/2 (Fig. 3), operated by A/SNorske Shell, was awarded in 1979. Blocks 31/3, 31/5, and 31/6 were awarded in 1983 with shared operatorship between Norsk Hydro a.s, Den norske stats oljeselskapa.s, and Saga Petroleum a.s.