Drillstem-Test Assemblies for Floating Vessels

Abstract

Improved drillstem-testing tools and procedures have significantly facilitated the difficult job of testing from Floating vessels. The equipment and methods described here, used successfully by one company in more than 200 tests in the Santa Barbara Channel, portend a new generation of tools for use in rough-weather areas. Introduction Drillstem testing has been used for many years to provide information that supplements electric provide information that supplements electric logging, mud logging, coring, and other formation evaluation techniques; in many cases, it provides critical data that cannot be obtained by any other method. The primary objective of drillstem testing offshore, as on land, is the acquisition of sufficient data to determine formation productivity and fluid content through the measurement of flow rates, bottom-hole pressures, and fluid properties. The mechanics involved in the testing are complicated by the motions of a floating vessel. To cope with this environment, several new tools have been developed: mudline safety valves, volume-balanced slip joints, slip-joint safety valves, and annulus-pressure-operated tester valves. The fail-safe design of these tools and the redundancy of the over-all test assemblies provide the necessary safety and reliability required offshore. The system is complex and requires the supervision of trained technical and operations personnel. Their training should include a study of the function and operation of each tool as well as of the over-all procedure. Although it would be desirable, it is not possible to detail a down-hole test assembly that would be optimum for all situations. Just as drilling procedures are tailored to meet the requirements of the well, a drillstem-test program should be designed to satisfy the information objectives, the safety considerations, and the economic realities. Besides, there is usually more than one service company available and capable of meeting these needs, and tools that have similar functions often differ in specific design and operation from company to company. The discussion that follows is based on one of the arrangements that has been successfully used by Exxon Company, U.S.A., in the Santa Barbara Channel and should explain principles applicable to floating test operations in general. Early testing of Channel formations onshore had been performed in open hole and the results were poor, both mechanically and economically. For improved reliability, the testing on the floating vessels was conducted in cased hole. Down-Hole Equipment A typical test assembly for a floating vessel is shown in Fig. 1. The bottom-hole portion consists of the following major tools (Fig. 2, from the bottom, reading up):Outside pressure recorders.Hookwall, compression set, tension release packer with integral bypass.Lower telescoping slip joints (total stroke, 12 ft, or about twice the maximum vessel heave). These permit a tester valve to operate by reciprocation without puffing tension on the packer.Reciprocal-type tester valve with sample chamber. JPT P. 851