Oil Production from Fractured Reservoirs by Water Displacement

Abstract

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. This paper was prepared for the 49th Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Houston, Texas, Oct. 6–9, 1974. Permission to copy is restricted to an abstract of not more than 300 words. illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussions may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. Abstract A study has been made of the flow behavior of fractured oil reservoirs produced by water displacement. A two-dimensional numerical model capable of simulating flow of water and oil in the matrix blocks as well as in the fractures has been developed. The validity of the model has been cheeked against data from a laboratory experiment involving a matrix-fracture system. Good agreement was observed between the laboratory and simulation results. By means of numerical simulation, the effects of production rate and fracture flow capacity on the production history and ultimate oil recovery of a fractured system have been evaluated. Results are presented for a single matrix-block system where the block is surrounded by horizontal and vertical fractures. Production rates ranging from 0.05 to 5 times Production rates ranging from 0.05 to 5 times the gravity reference rate of the matrix, and fracture flow capacities ranging from 0.1 to 10 times the flow capacity of the matrix are included in the investigation. At production rates much lower than the gravity reference rat the system behaves essentially as a nonfractured reservoir. It is also observed that for fracture flow capacities of the order of one-tenth of the matrix flow capacity, the effect of the fractures is negligible. At higher fracture flow capacities the water-oil ratio performance of the system becomes increasingly more sensitive to production rate. Water production starts much earlier with high fracture flow capacities and high production rates than it does from a nonfractured reservoir, and a large portion of the oil is produced at high water-oil portion of the oil is produced at high water-oil ratios. However, if the additional water can be handled economically, no oil is lost by high rate production. It is demonstrated that for a given fracture flow capacity, the producing water-oil ratio is a unique function of oil remaining in place and present producing rate. Thus, a reservoir can be produced at a high rate until the water-oil ratio becomes too high to handle. Then, reducing the rate causes the water-oil ratio to decrease to the value it would have had if all the oil had been produced at this lower rate. Introduction A significant number of petroleum reservoirs exist where discontinuities such as fractures or joints in the porous rock matrix are the main paths for transmitting fluids to the producing wells. In naturally fractured producing wells. In naturally fractured reservoirs, the matrix rock generally has a low permeability and one or more well-developed permeability and one or more well-developed fracture systems are present.