Cleaning Effectivity of Concentric Coiled Tubing in Horizontal Wells, Cerro Negro Area, Carabobo Field, Venezuela

Abstract

Abstract The Orinoco Oil Belt is the largest heavy oil accumulation in the world with 1.2 trillion of in situ reserves in an area of 54.000 square kilometers covering the southern portions of three states in the Eastern Venezuela Basin. Carabobo is one of its more prospectives areas with very thick sands with excellent petrophysical properties. The study area has 120 square kilometers corresponding to the Extraheavy Oil Unit of the Morichal District, Monagas State. In the early 80s explotation began in this area with drilling of 150-300 meters spaced vertical wells. Further secondary recovery method (including alternate vapor injection) evaluations were conducted in order to enhance a more commercial production. In late 80s and early 90s the new uprising drilling technology was used in the area, with 400 meters spaced deviated and inclined wells where further alternate vapor injection was applied. In the late 90s and 2000s drilling campaigns of horizontal wells and multilateral wells, respectively, were performed in the study area, with very dense drilling of heavy and extra-heavy oil sand reservoirs with horizontal wells of extended section that generated a very problematic large sand production. Thus, reaconditioning and cleaning up of these wells was needed in order to optimize oil and sand production within desired levels avoiding the damage of equipments after completion. Cleaning up of horizontal wells gets difficult due to circulation loss, high permeabilities and low reservoir pressure; therefore use of the 2 3/8" tail tubing was substituted by the new Concentric Coiled Tubing (CCT) technology and a Vacuum pump. CCT was tested in selected wells where it was used; evaluating parameters such as oil sand petrophysics, production behavior, cleaning up services conditions and associated costs during productive life of wells. The main results of using CCT are prolonging recurrent sanding that implies short term recurrent cleaning up services, avoiding additional expenses in repair services, equipment replacements or well closure among other disadvantages. Repair services result in money waste, disturbance of routine operational field activities and subsequent costs increase of produced barrel due to restrictions in production. Economic indicators have shown evident rentability of using this tool in horizontal wells of Extraheavy Oil Unit of Morichal District.