NOTICE CONCERNING COPYRIGHT RESTRICTIONS

Transcription

1 NOTICE CONCERNING COPYRIGHT RESTRICTIONS This document may contain copyrighted materials. These materials have been made available for use in research, teaching, and private study, but may not be used for any commercial purpose. Users may not otherwise copy, reproduce, retransmit, distribute, publish, commercially exploit or otherwise transfer any material. The copyright law of the United States (Title 17, United States Code) governs the making of photocopies or other reproductions of copyrighted material. Under certain conditions specified in the law, libraries and archives are authorized to furnish a photocopy or other reproduction. One of these specific conditions is that the photocopy or reproduction is not to be "used for any purpose other than private study, scholarship, or research." If a user makes a request for, or later uses, a photocopy or reproduction for purposes in excess of "fair use," that user may be liable for copyright infringement. This institution reserves the right to refuse to accept a copying order if, in its judgment, fulfillment of the order would involve violation of copyright law.

2 DEVELOPMENT OF A WIRELINE BLOWOUT PREVENTER FOR USAGE ON PRODUCING VAPOR-DOMINATED GEOTHERMAL WELLS Raymond E. Roesner and Tom A. Garney Dresser Atlas, Dresser Industries, Inc. Houston, Texas ABSTRACT A reliable, low maintenance wellhead control system to support logging services in producing geothermal wells has been developed by Dresser Atlas in cooperation with Bowen Tools, Inc. Two hydraulic wireline blowout preventers (BOP'S) were stacked in series over a well's master gate valve. Their internal components were modified to withstand steam flowing at 26OoC (5OO0F), 3.45 MPa (500 psi). The BOP was incorporated with an advanced four-valve pressure equalization and monitoring system. High temperatures called for special hydraulic fluid and severe service pressure gauges. For safety, a pressure/temperature monitor and grease pack-off were added. This new Geothermal Wellhead Control System proved itself in field tests earlier this year. INTRODUCTION As a prerequisite for conducting wireline services on geothermal wells,* it would be necessary to possess a wellhead control system capable of operating under geothermal conditions. At first, this system consisted of conventional wire1 ine blowout preventers (BOP'S) equipped with a standard lubricator. However, these units proved to be no match for wells that produced 1 ive steam at 26OoC (5OOOF). It was for this purpose that the Geothermal Wellhead Control System was developed. This system consisted of three basic sub-systems: the Geothermal Wi re1 ine Blowout Preventer (Geo-BOP), the BOP Control System, and the Geothermal Lubr i cator. Fig. 1 During the development of the Geo-BOP, the first elastomer used under actual geothermal cond i t ions was ethylene propylene rubber (EPR). This material proved to be unsatisfactory due to substantial physical degradation. Inner seals (Fig. 2) made of EPR were extremely susceptible to erosion caused by the flowing steam of a producing well. This caused material to be removed from the sealing faces which made it impossible for a seal to form around the logging cable. GEOTHERMAL WI RELINE BLOWOUT PREVENTER The heart of the Geothermal Wellhead Control System was the Geo-BOP. This unit is made up of two Bowen Tool Universal Wireline Blowout Preventers stacked in series (Fig. 1). fr Geothermal Well shall henceforth be defined in this paper as a well which is capable of producing flowing steam at 26OoC (500OF), 3.45 MPa (500 psi). 593

3 Roesner et a1. Success came when the inner seal material was changed to a tet caf 1 uoroethyl ene (TFE) compound. The new TFE inner seals resisted the errosive forces of the flowing steam and continued to provide an acceptable seal after repeated usage. However, ram pressures had to be increased in order to get the TFE compound to energize in the same manner as an elastomer compound. This made hydraulic operation imperative. As a safety precaution, silicon oil replaced standard hydraulic fluid, which has a flash point lower than the wellhead operating temperature. The final internal modification was a fluoroelastomer used to make up the outer ram seals and O-Rings. GEO-BOP CONTROL SYSTEM Due to the extremely hostile environment in which the Geo-BOP must operate, it was necessary to develop an improved BOP Control System. This control system consisted of four individual subsys tems : 1. Pressure Equalization System 2. Pressure and Temperature Monitoring System 3. Grease Pack-Off System 4. Hydraul ic Operat ions System Presrure_Esuall~a~io~-~Y~~~ The purpose of the Pressure Equalization System was to enable various sections of the wellhead to be pressurized or de-pressurized at will (Fig. 3). The Pressure Equalization System connected the upper and lower rams, the center cavity of the Geo-BOP, and the Lubricator to the we1 1 head.!!?l%?-lo9is Valve VI allows wellhead pressure to flow into the Pressure and Temperature Monitor. Valve V2 allows Lubricator pressure to flow into the Pressure and Temperature Monitor. Valve V vents pressure from the center cavity of the $eo-bop into the Lubricator. Valve V4 vents pressure from the center cavity of the Geo-BOP during grease injection. Valve V1 and V2 allow wellhead pressure to pass i'nto the Lubricator, thus equalizing the pressure above the upper ram and below the lower ram. Valves V1, V2 and V allow complete pressure equal ization betwee2 the upper ram, the lower ram, and the center cavity of the Geo-BOP. This eliminates any differential pressures across the rams. Before opening the rams, all differential pressure across the rams had to be relieved. Failure to do so would have resulted in severe damage to the inner seals. This Valving System served to promote safe operations by removing - all pressure from the Geo-BOP. Pressur~_a?d,Temeer~~~re-~~~~~~r~~g-~ys A system to monitor the pressure and temperature of the wellhead was used on the Geo-BOP. This system consisted of a strain gauge pressure-transducer in conjunction with an integral thermocouple (Fig. 4). These nstruments were then connected to a portable readout unit located conveniently on the wellsi e. CENTER CAVITY TEMPERATURE MONITOR Fig. 3 HEAD Fig. 4 A sealed strain gauge type pressure-transducer was used instead of a Bourdon Gauge because suspended particles could not infiltrate the strain gauge mechanism. On the other hand, 594

4 Koesner, et al. the Bourdon mechanism would be rendered inoperative after continuous service. The thermocouple operated at the sensing face of the strain gauge. This resulted in accurate pressure readings by calibration of pressure with respect to temperature. The Grease Pack-Off System was an added safety measure. This system used the center cavity, (Fig. 1) which exists between the upper and lower rams, to form a secondary seal. The purpose of this seal was to block minute pressure leaks which the inner and outer seals could not totally prevent. --. This system consisted of an air-powered grease injector using high temperature N.L.G.I. #1 grease and high pressure delivery hose connected to a grease injection nozzle. allowed the high temperature wireline to pass into and out of the well without substantial wellhead pressure losses. Mounted on the Geo- BOP (Fig. 6), this special unit consisted of a 14 CM (54") ID Bowen Lubricator with screw type unions. Two valves were included for venting pressure on the lubricator only. A control head on top of the lubricator formed a seal around the cable to restrict the flow of steam while the well was being logged. Fluoroelastomer O-Rings and line wipers were substituted for standard rubber parts. The grease injection nozzle was made up of two main parts,.08 MPa (12 psi) differential check valve and 34.5 MPa (5,000 psi) severe service gauge (Fig. 5). Fig. 5 In the event of a seal failure in the lower ram, the check valve would prevent wellhead pressure from flowing back into the grease injection system. The check valve, mounted at all times on the Geo-BOP, allowed the Grease Injection System to be disconnected while the Geo-BOP was under pressure. The 34.5 MPa (5,000 psi) gauge, mounted on a quick disconnect, monitored the grease injection pressure and the center cavity pressure. Thus, it was necessary to have the gauge in place only during operation. When not in operation, the grease delivery hose could also be removed. HYdraulkOeerafh $ - S_yst~ First, due to the high wellhead operating temperatures, it was necessary to isolate the hydraulic hoses from the Geo-BOP, This was accomplished both with mechanical push-off devices and with tubing extensions added to the hose ends. Second, due to the higher ram pressures, it was necessary to use 34.5 MPa (5,000 psi) severe service gauges on the pumping units. GEOTHERMAL LUBRICATOR The Geo-Lubricator, a modified Bowen device, Fig

5 Roesner et al. SUMMARY Substitutions were made for various elastomeric components inside the Geo-BOP. Thus, the Geo-BOP could operate longer before a rebuild would become necessary. The combination of pressure equalizer, pressure and temperature monitor, and grease injector added a substantial safety factor to the system. The Geothermal Wellhead Control System was successfully tested at the Castle Rock Springs Geothermal Field in the spring of ACKNOWLEDGEMENTS We thank W. L. Daniel of Dresser Atlas, Dresser industries, Inc., Roger Chancey and Ray Bozart of Bowen Tools, Inc. for their cooperation and assistance in this project. 596