Effect of Abnormal Pore Pressure on Deep Water Drilling

Abstract

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. This paper was prepared for the SPE-European Spring Meeting 1976 of the Society of Petroleum Engineers of AIME, held in Amsterdam, The Netherlands, April 8–9, 1976. 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 publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor 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. Abstract Drilling operations in deep water are more constrained than on land. Apart from sophistications concerning control systems, hardware, etc. this is caused by the convergence of mud and formation strength gradients, the weakness of shallow formations, the possible small margins between formation strength and pore pressure and the mud weight pore pressure and the mud weight capacity of the riser system. As a result of these constraints, the ultimate well depth would be severely limited when encountering abnormal pressures. In order to investigate this pressures. In order to investigate this problem a survey was carried out on problem a survey was carried out on formation strength and abnormal pore pressure occurrence. The outcome of it pressure occurrence. The outcome of it suggests that the majority of deep water wells can be drilled with conventional casing systems. Mud weights required to control abnormal pore pressures will cause fracturing of the formation more readily in deep water than in land operations. A solution to this problem has not yet been found. Consequently prediction and early detection of abnormal pore pressures is of greatest importance for deep sea operations. Introduction Formation strength, expressed as fracture pressure, is lower at any given depth below derrick floor in deep water than in shallow water or land drilling operations. This is caused by the fact that in wells located offshore a part of the overburden consists of water rather than of sediments. As a result there is an interval above the intersection of the formation strength and mud gradients in which the mud pressure exceeds the formation strength. In order to avoid fracturing, casing will have to be set prior to raising the mud weight.