New Reservoir Testing / Sampling System Reduces Costs and Improves Real-Time Data Acquisition in Deep Water and Environmentally Sensitive Wells -GOM Case Histories
Authors: Salguero Mario Alejandro , Almanza Edgar A. , Kool Henk 
Published: October 2008

The use of drill-stem testing (DST), particularly in offshore environments, has seen a marked decline in recent years. Several factors such as escalating rig rates, environmental concerns, personnel safety, and drilling-rig deck-space requirements have been responsible, but other factors have also contributed to this decline. Other testing methods have been developed that have been capable of providing certain types of reservoir information more cost efficiently and during a shorter period of time. This paper discusses a new type of system that allows a prospect to be sampled and tested without the necessity of a comprehensive and extended well test, or the testing process can be used as a first testing phase to be followed by a complete DST or production test, if necessary.

Since closed-chamber tests were introduced in 1977, variations of this testing technique have been used to provide good flow estimations and basic reservoir parameters, although build-up data with short producing times were difficult to analyze. Combining this method with back surge proved to be very useful for perforation cleaning. However, some conventional sampling and data-collection systems in heavy oil and unconsolidated reservoirs have had limited success, resulting in decisions concerning assets to be made with limited information.

The development of new bottomhole tools, either for testing or sampling, as well as real-time data acquisition systems and bottomhole data analytical methods are now available for short-time tests and offer an alternative for reservoir testing that can be completed in shorter testing times and are environmentally acceptable. They are also more effective in a broader scope of environments.

The focus of this paper is one of these techniques that can be used in prospects where:Expected production does not support the implementation of full-scale well-test evaluation and the data provided can be used to properly design an operation for full evaluation.Environmental issues limit the oil and gas flaring as in some offshore wells or rain-forest locations.Remote locations are not conducive to equipment transportation or have limited footprint.

This document describes the first jobs performed with this limited-emission system in deepwater Gulf of Mexico in heavy-oil unconsolidated sandstone and in high-viscosity oil environments in Brazil. No safety incidents and no environmental incidents occurred. The system successfully captured bottomhole samples with pressure-volume-temperature (PVT) quality and sufficient reservoir information to calculate reservoir pressure, relative permeability, and radius of investigation on both cases presented. Both examples met all test objectives and demonstrated the advantages of the system.

Introduction

Traditionally, fully blended DSTs have been used to acquire bottomhole pressure and temperature and perform sampling operations. The system described in this document minimizes the potential environmental impact from surface fluid handling during these operations, making the work more environmentally friendly, reducing risk, and increasing safety. In addition, the use of the advanced sampling and data-collection systems now available for heavy oil and unconsolidated reservoirs has increased the performance of data acquisition and characterization information.