Abstract

The Orinoco Belt in Venezuela contains the largest known deposits of heavy oil in the world. Estimates for proven reserves are estimated to be 1.2 trillion barrels of oil-in-place (STOOIP) and the field covers an area of 5400000 hectares (54000 km2) across three states in Eastern Venezuela. Drilling in the area started in 1953 and over the years new technologies like horizontal drilling have made possible the economic exploitation of previously heavy oil plays. BITOR, a subsidiary of Petróleos de Venezuela S.A. (PDVSA), is an operator in the Cerro Negro field located near Morichal in Monagas State, Venezuela. Recently, Cerro Negro is developed only by horizontal wells, completed with a slotted liner / open hole horizontal. Over time the horizontal section has been increased to improve production, however this has also made it more difficult achieve a clean well. Conventional methods to remove filter cake and drilling fluids were not effective and caused downhole pump problems and formation damage.

Recently a new coiled tubing technique has been devised to clean wells by means of a hydraulic jet pump. The pump creates a pressure drop across the formation sandface and unwanted fluids, polymer residues and solids are transported to surface. This technique is ideally suited to horizontal heavy oil reservoirs where pressures are low and viscosity is high. The technique makes use of Concentric Coiled Tubing (CCT) and a special Vacuum Tool (VT) designed to apply a specific and controllable drawdown. Several jobs were performed on wells in the Cerro Negro with outstanding results. Post job analysis of vacuumed wells has revealed improved bottom hole flowing pressure and increased production compared to non-vacuumed wells. Moreover, analysis of fluid returns shows that significant amounts of polymer residue as well as both drilling and formation solids are being cleaned from the face of the completion.

This paper illustrates the usefulness of CCT vacuum technique and several complementary technologies now being applied. A comprehensive technical review and case study of work performed in the Cerro Negro field are also presented.

Introduction

There are four major fields in the Orinoco Belt. From West to East they are; Machete, Zuata, Hamaca and Cerro Negro (See Figure-1). In terms of legal company type, these are considered Strategic Associations (SA) and each field has a primary operator. PDVSA is a partner in all of these projects.

The Cerro Negro field is composed of: PDVSA and Cerro Negro Operator (Mobil and Veba-Oil). BITOR, is a subsidiary of PDVSA, which is responsible for the exploitation and emulsification of natural bitumen (extra heavy oil), as well as supply and marketing of Orimulsion®, which is produced from this natural bitumen. The BITOR concession is located near of Morichal field, in the most eastern section of the Orinoco Belt. The Cerro Negro field was discovered in 1979 and has 382 wells. Currently, a total of 250 wells on production.

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