Effect of Formation Damage, Length and Reservoir Thickness on the Inflow Performance of Horizontal Wells

Abstract

Abstract Horizontal wells offer many advantages, compared to vertical ones. However up to now, their performance did not always live up to expectation especially in the Middle East where vertical wells are commonly naturally prolific. This has been attributed in general to near well bore formation damage. Because of their large contact area of reservoir rock, horizontal wells are more susceptible to drilling and workover induced formation damage than vertical ones. The effect of skin damage on horizontal wells has been abundantly discussed in the literature; however, the method of handling the calculations varies from one author to the other. In most cases, the authors did not take into consideration friction, the variation of skin along the horizontal section of the well and the perforation distribution. It is common now to drill very long horizontal wells where the skin may vary along the well. Therefore, it is important to estimate the real contribution of the different sections of the horizontal well to the total production of the well and the role of formation damage and friction in the overall performance of the well. The present paper addresses the case of highly permeable reservoirs displaying variable skin along the horizontal section of the well. Friction losses as well as perforation distribution are taken into account. A literature survey is conducted in order to understand the role of formation damage and friction. A semi analytical approach is used to study the simultaneous effect of perforation distribution, near well bore formation damage and friction losses on the production of horizontal wells. The results show the effect of various well parameters such as well length, anisotropy ratio, skin and perforation distribution on the inflow performance of the horizontal well. The study shows particularly that: For short horizontal wells, formation damage does not significantly penalize horizontal wells. This is particularly true for thin reservoirs. For medium horizontal wells: ·For thin reservoirs, formation damage moderately affects the production of horizontal wells. For example, for the case studied, where the skin S=10, the production loss is only about 20% while for S=30, the production loss is 45%.·For thick reservoirs, the situation is not the same. For example, the production loss of a damaged well with a skin of 10 is about 70% and the production loss of a damaged well with S=30 is almost 95%. For long horizontal wells: ·For thin reservoirs, the production loss due to formation damage is still not excessive. It is only 35% for S=10 and about half when the skin reaches 24.·For thick reservoirs however, horizontal wells become very sensitive to formation damage. Even for a skin of 10, the production loss may exceed 95%. The larger the fraction of the well open to production, the more severe is the impairment.