Assessment of Jet Perforated Rock Damage by Finite Element Method

Abstract

Abstract Finite element method has been employed to evaluate stress distribution within the sandstone formation as the result of a perforation job. The study is based on the followings: a radial reservoir with a perforated well located at the center of the reservoir, characteristics of both 3.5 and 10.5 gr. RDX charges, and the mechanical and thermal properties of the Berea sandstone. This research was performed in three distinct steps: 1) jet temperature effect, 2) jet pressure effect, and 3) combined jet temperature and pressure effects. The results indicated that a 3,5 RDX charge with 2,500,000 psi initial pressure is capable of disturbing rock formation up to five inches longitudinally and two inches radially. The extent of this damage zone for a 10.5 gr. RDX charge having an initial pressure of 4,000,000 psi is eight inches longitudinally and four inches radially. The linear effect is within the first few inches of the perforation runnel entrance. Within this region, rock grains are under an intensive sudden shock pressure wave of 2 to 4 million psi for fraction of a microsecond As a result, rock physical structure will change to metamorphous with a lower bulk density than that of un-shocked rock, causing a sudden decrease in formation porosity and hence formation permeability. This study however, shows that thermal stresses as the result of jet temperature (1,200°F), is insignificant.