Abstract

Completing horizontal wells with openhole sections or non-cemented liners is a common practice. This type of openhole wells is preferred to maximize reservoir productivity. Some questions that always come up for this type of wells are: will it be necessary to cleanup the mud and filtercake from the openhole section before or while starting production? Will the filtercake disperse and get removed while producing the well and applying drawdown to the formation? Will the remaining filtercake impair well productivity?

The paper presents the case of a gas producing horizontal well in Indonesia completed with a perforated liner. The target reservoir is a clean sandstone reservoir. The horizontal drain is 1155 feet (ft) long. The reservoir permeability is ranging between 0.1 and 5 millidarcies (mD)

An engineered oil-based mud was used as drill-in fluid to prevent any damage to the reservoir. A carbonate particle-based filtercake was used to create a thin and reliable filter cake. While drilling this well, it was believed that reservoir damage was minimized. It was also believed that there would be no need to cleanup the mud and filtercake left in the hole and that the well would cleanup by itself easily once it started producing.

After disappointing production results from this well, zero production was achieved, a decision was taken to investigate the effect of the mud on well productivity, consecutive interventions were planned to remove one potential damage mechanism at a time and investigate the effect on well performance. Upon the completion of all the intervention steps, the well started to produce. A pressure buildup test performed one month after the intervention showed that the well was producing with a damage skin value of zero.

The different interventions, the laboratory results and the effect of each taken step on well productivity are discussed in this paper. Overall results of the interventions will be shown and a complete solution for bringing new openhole horizontal wells into production will be proposed.

Introduction

The Tambora field lies in the swamp environment of the upper Mahakam delta, six miles south of Badak/Nilam. Tambora is now primarily a gas field, although there are small oil rims to the north (produced before 1990). Tambora field is operated by TOTAL E&P Indonesie as part of their operations in Indonesia's East Kalimantan region. In the same region, TOTAL is also operating Tunu, Peciko, Bekapai, Handil and Sisi-Nubi fields. TOTAL is the major contributor for gas production in the region. Fig. 1 shows a map of the different fields location.

The Tambora field produces from a series of interbedded deltaic sandstones, shales, coals and locally limestones. These formations are classified into four main zones: D, E, F and G.

The G reservoir is characterized by its low permeability. Its productivity while produced through vertical wells is low and deemed not satisfactory. For this reason, development of this field through horizontal openhole drains is necessary to achieve acceptable level of production.

Openhole completed reservoirs will lead to higher productivity index but usually damage due to drilling mud is a concern. During the recent years, mud systems evolution was remarkable. The objectives are to achieve:

  • Very low leakoff to the reservoir by the design of optimized filtercake, this will prevent the reservoir damage due to mud invasion,

  • Easy removal of the filtercake by applying a minimum drawdown to the formation. This will enable maximum productivity from the reservoir without any potential need for a stimulation intervention.

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