Determination Of Pore Volume In A Naturally Fractured Reservoir

Publication Rights Reserved This paper was prepared for the 40th Annual Fall Meeting of the of the Society of Petroleum Engineers of AIME, to be held in Denver, Colo., Oct. 3–6, 1965. 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 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. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. Conventional methods for estimating original oil in place are not suitable for reservoirs where the oil is contained primarily in a natural fracture system. A method has been developed based on theoretical considerations which uses empirically derived values for needed coefficients. These values can be obtained from pressure interference and productivity well test data. The Mississippian-Solid formation has been diagnosed as a "pore space in fractures" type formation. The S. W. Lacey Field, Kingfisher County, Oklahoma, was the site of a special well test program designed to estimate hydrocarbon pore volume in a typical Mississippian-Solid reservoir. After a 45-day shut-in period, one well was put on controlled production and continuous bottom hole pressures were registered for 51 days at three of the five nearby shut-in offset wells. Pressure communication was established with one of the observation wells located 5000 feet from the producer. A pressure drop was not recorded at either of the other two wells. Where interference data were obtained, it was used to provide numerical values for solving the theoretically derived equations. A calculated oil in place of 6515 Res. Bbls/ acre was obtained as representative of the formation in the vicinity of the observation test well. This information together with the original productivity index of this well was used to calibrate, for this field, a theoretical relationship between fracture volume and fracture flow capacity. From this relationship, the original oil in place for other parts of the field may be estimated. In application, the fracture storage capacity is derived from the well's initial productivity index. Where measured productivity data were not available, a method was used which obtained productivity index values from an empirical correlation which related these values to reported original producing rates. The method used is expected to provide acceptable results because most wells in the S. W. Lacey Field were initially potentialed using about the same backpressure. The paper does not include a study of the expected oil recovery performance from this unusual reservoir.