石油および環境バイオテクノロジージャーナル

概要

Geomechanics Modeling and Tensile Failure in Karstified Dammam Formation

Jawad Alshakban*, Wafaa Al-Shatty, Doaa Albaaji, Raffaele Romagnolid

Dammam is one of the most tiresome formations that drillers challenge while drilling in the oil fields which located in South of Iraq and North of Kuwait. Therefore, the development of a geomechanical study may play a meaningful role in identifying the causes and establishing appropriate solutions to minimize the drilling cost. This research paper is to define the geostatic stresses, pore pressure, rock mechanical strength, elastic modulus and build one-dimensional mechanical earth model utilizing the most common failure criteria; Mohr-Coulomb, Mogi Coulomb and Stassi d’Alia. The best failure envelopes which anticipated the shear failure are Mogi and Stassi d’Alia in contrast with Mohr, while all criteria accord the same results with respect to the tensile failure. No laboratory test such as triaxial, uniaxial and Brazilian tests are available to be utilized for calibration purposes, for that reason the only log derived parameters have been employed to construct the Mud Window (MW). MW assists determining the maximum mud weight to avoid drilling induced tensile failure while cementing and overbalanced drilling. The same thing regarding the horizontal stresses, no leak of test or hydraulic fracture data are obtainable to match the geostatic horizontal stresses. On the other hand, measured pore pressure at two points of different intervals within the formation was exploited to accommodate the predicted pore pressure. However, many empirical equations are available to define the pore pressure from sonic and resistivity logs as well as from seismic velocity modeling. Eaton sonic technique was the most appropriate equation to anticipate the pore pressure especially at young basins; therefore it was adopted to establish a continuous profile of pore pressure along the Dammam interval.