A Field Trial to Test Fiber Optic Sensors for Downhole Temperature and Pressure Measurements, West Coalinga Field, California

Abstract

Abstract A field trial to test fiber optic sensors for temperature and pressure measurements was completed in two temperature observation wells in a steamflood area of the West Coalinga Field in Coalinga, California. Objectives of the trial were to test a novel hydraulic deployment system that can easily install and retrieve fiber optic sensors from wellbores and to test the data quality from a fiber optic Distributed Temperature Sensor (DTS) and a pressure sensor. Deployment of the temperature and pressure fiber optic sensors was successfully demonstrated by using the hydraulic deployment technique. Excellent data correlation was obtained between the DTS and the conventional wireline conveyed temperature survey tools. Similarly, the pressure sensor showed impressive resolution and dynamic response capabilities. Since the fiber optic system has the capability of providing continuous reservoir temperature and pressure data, reservoir management in primary or assisted recovery projects can be improved. Introduction The objectives of this field trial were threefold:first test a hydraulic deployment system whereby a thin fiber optic cable can be deployed and retrieved easily.test a Distributed Temperature Sensor (DTS) for data quality and reliability of obtaining temperature profiles in a high temperature environment.test a fiber optic pressure sensor in a high temperature environment. The pressure sensor, which was simultaneously deployed with the temperature sensor in a closed system, was tested by applying pressure from the surface. The performance of both systems proved very effective and provided high quality data in a high temperature environment. The field trial took place in the West Coalinga Field. The Field is located on the west side of the San Joaquin Valley approximately 100 miles northwest of Bakersfield, California. Field production is primarily heavy crude (12 to 15 API) from the Miocene Temblor Formation. The target reservoir consists of two sand layers separated by a shaly layer. The sands are unconsolidated with an average porosity in excess of 30%, an original oil saturation ranging from 45% to 55%, and an average air permeability of approximately 800 millidarcies horizontally. The upper sand layer averages 45 ft. in thickness, while the lower sand is about 35 ft. thick. Steam injection in this reservoir was initiated in October 1988 and is ongoing today. Production from the constituent reservoir sand layers is enhanced by steam injection through a single tubing string. Permeability variations between the two sand layers resulted in uneven processing over major portions of the field. Since steam injection costs are the highest of all operating costs, it is critical to manage heat distribution in the reservoir properly. P. 351