Research On Rational Working System Of Horizontal Wells In Low Permeability Reservoirs

The low permeability reservoirs are widely distributed and developed by advanced drilling and producing technologies, consolidating their positions in current and future reservoir exploitation. However, low permeability reservoirs often present low permeability and poor formation connectibity as well as quick pressur decline after production, resulting in unsatisfied economic profit. As a kind of practical development well shape, horizontal wells can provide larger drainge areas during production, having an edge in providing higher output. With the aid of horizontal wells, the exploitation cost for low permeability reservoirs has become much lower and more economic effective. Under the context of continued crude oil decrease in the world market, development methods and corresponding working systems are need to be optimized in order to achieve higher economic efficiency and larger oil output.Facing the problems of low production and high development costs, this reseaech studied the inflow performance relationship of low permeability reservoirs. As for natural flowing wells, the maximum production under different water cuts and critical water cut are studied. As for rod pumping wells, reasonable suction parameters are analyzed. As for intermittent pumping wells, reseonable working systems are selected. Based on the above methods, this paper achieves following achievements:(1) Considering threshold pressure gradient, the oil-gas two-phase inflow performance relationship for horizontal wells is established through Joshi's horizontal wells productivity equation. Using Petrobras's vertical wells productivity equation of oil-gas-water flow, the oil-gas-water three-phase inflow performance relationship is established and the threshold pressure gradient is taken into account as well;(2) The flow pattern for vertical section and deviated well section of well bore are relatively classified. Through calculating pressure distribution along well depths and analyzing inflow performances, the maximum production under different water cuts and the critical water cut of given production are obtained for natural flowing wells;(3) Based laws of fluids flowing in the wellsbores of pumping unit, facters influencing pump efficiency are analyzed. Then taking the optimized economic efficiency as the targert, reasonable suction parameters for pumping wells are studied;(4) Aiming at the problem of low pumping efficiency after a period of production time, without additional investment, variation laws of wellbores liquid levels during opening and shutting-in wells, liquid producing rules and unloading rules for pumps are relatively studied. Moreover, reasonable working systems for intermittent pumping wells are studied.In conclusion, this research can provide both theoretical and practical basis for analyzing dynamic inflows and outflows performances. This paper can also lay foundation for selecting resaonalble working systems for wells under different production methods.