Abstract

Cantarell field produces a significant portion of the total oil production of PEMEX. Over the past few years, Cantarell oil production has been declining, mainly because of the maturity of the field. Sustaining oil production at current levels is a constant challenge for PEMEX, which is also attempting to increase exploration. One of the main challenges involves an increase in water production, which has led to wells being temporarily shut in until a workover rig becomes available. This waiting time could be years. Meanwhile, PEMEX is investigating alternative solutions to optimize rig utilization and offshore rigless workover options.

Recently, coiled-tubing-conveyed inflatable packers have become a key enabler when performing workover operations while the production tubing remains in place, which enhances timely and cost-effective intervention solutions. Through-tubing inflatable packers have successfully isolated zones during water-control treatments, cementing operations through coiled tubing (CT), and permanent zonal abandonment, thus enabling the operator to perforate the upper oil-bearing zones. The use of through-tubing inflatable packers for zonal isolation is now featured in the rigless workover plan for several wells, which is expected to deliver a significant increase in oil production.

This paper examines these recent applications of through-tubing inflatable packers in the region and presents the relevant well conditions and the criteria used for selection. It provides case histories and best practices from several through-tubing applications. Recommendations for job design, auxiliary equipment, and personnel competency are thoroughly discussed.

Introduction

Cantarell basin is located 75 km northeast of Ciudad del Carmen, Campeche. The field was discovered in 1975 with the perforation of well Chac-1. Quickly, Cantarell became the largest contributor of Mexican oil production.

Cantarell has six producing fields, Akal, Nohoch, Chac, Kutz, Sihil Ligero, and Sihil BTPKS. The producing formation is mostly naturally fracture dolomite with average permeability up to 4000 md, and a 600 m. net pay. The produced fluids are typically 22-degree API oil, with a 65 m3/m3 gas/oil ratio (GOR) and an average reservoir pressure of 1350 psi. The field production is assisted with gas lift because of the low pressure of the reservoir.

By 1995, a total of 152 wells were producing, and the formation pressure started to drop dramatically. In 2000, PEMEX launched a very ambitious project, including the drilling of 213 wells, the development of a nitrogen injection complex to maintain the reservoir pressure, and modernization and building of new infrastructure. As a result of this project, in early 2003, the field reached its maximum historical daily production, which has been declining since then.

Actually, the Cantarell basin already has 418 wells drilled, 205 of them are producing, and more than 100 wells are shut in, scheduled for workover. The operator has 28 satellite platforms with only 20 drilling/workover rigs to intervene them. Then, effective asset utilization as well as rigless intervention is mandatory to maintain the actual production levels.

Some of the problems that the field has been experiencing are water invasion on the lower oil-bearing zones and high GOR and N2 content on the upper oil-bearing zones. In most cases, the workover objectives involve plugging the invaded zones to produce another zone.

The traditional procedures for change of intervals with workover rig include:

  • Temporary zonal isolation (to act as second barrier for Christmas tree removal).

  • BOP and rotary table installation.

  • Production tubing pull out of hole (POOH).

  • Permanent zonal isolation.

  • Production tubing runs in hole (RIH).

  • New zone perforation.

  • Kickoff.

  • Deliver well to production facilities.

Zonal isolation can become very difficult for several reasons: poor cement bond behind the casings, returns cannot be attained on surface because of the low reservoir pressure, and the huge permeability on the open zones prevents effective control on fluid placement. The same problems are experienced when zonal selective treatments are pumped.1

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