Results Of Reservoir Engineering Tests, 1977, East Mesa, California
Authors: Narasimhan T.N. , Schroeder Ron C. , Goranson Colin B. , Benson Sally M. 
Published: December 2007

The East Mesa KGRA (Known Geothermal Resource Area) is located in the Imperial Valley of Southern California. Geothermal fluids at temperatures of 160 degrees C to 177 degrees C have been successfully tapped by fourteen geothermal wells, ranging in depth from 1800 to 2800m. During 1977 several production and interference well tests were performed on the East Mesa wells in order to assess the reservoir potential. The results of these tests are summarized in this paper.

Introduction

The East Mesa KGRA (Known Geothermal Resource Area) (Figure 1) is located in the Imperial Valley of Southern California close to the Mexican border. In addition to the U.S. Bureau of Reclamation (BUREC) which owns lands in the central part of the geothermal anomaly, two private companies have leased lands for the exploitation of the geothermal fluids: Republic Geothermal, Inc., to the north and Magma Power Co. to the south. By late 1977, a total of fourteen wells had been drilled to explore the resource: five by the BUREC, six by Republic and three by Magma. Lawrence Berkeley Laboratory has been carrying out well tests since early 1976 in order to assess the characteristics of the East Mesa geothermal reservoir. The results of tests conducted during 1976 have been discussed elsewhere. The purpose of this paper is to present the results of the well tests conducted during 1977. These tests, carried out in collaboration with BUREC and Magma (February to June, 1977) and with Republic (July to October, 1977), included production and interference as well as injection tests. Valuable information was obtained concerning the reservoir parameters and geometry. This paper, however, will parameters and geometry. This paper, however, will focus attention primarily on the interference tests. Injection tests are outside the scope of its presentation. presentation.

GEOLOGY

The East Mesa resource occurs in a young (tertiary and geologically active sedimentary basin filled with over 6,000m (20,000 feet) of sandstones, siltstones and shales. Structurally the basin is considerably faulted within the East Mesa area. At lest three faults, varying in trend from NNW-SSE to WNW-ESE, have been positively identified. Growth faults, penecon-temporaneous with deposition and trending northeast penecon-temporaneous with deposition and trending northeast have also been inferred (J.L. Smith, Republic Geothermal Co., personal communication). There is reason to believe that some of the faults may be discontinuous, either laterally or vertically. The disposition of isotherms at a depth of 1,800m (6,000 feet) suggest that the hot-spot of the geothermal anomaly is centered in the BUREC property (Figure 2). The wells tested vary in depth from 1,800m (6,000 feet) to a little over 2,770m (9,000 feet). The well-head temperatures, which are dependent on flow rates, varying from 160 degrees C (320 degrees F) 177 degrees C (350 degrees F). All the wells are under artesian head with well-head pressures ranging from 3.4475 × 10 Pa (50 psi) to 8.274 × 10 Pa (120 psi). The available data on the different wells at East Mesa are summarized in Table 1.

DESCRIPTION OF WELLS TESTS

The tests were conducted in two parts. The first part, extending from February to June 1977, consisted part, extending from February to June 1977, consisted of producing BUREC Wells 6-2 and 6-1 for over 10 weeks and monitoring pressure drawdowns in BUREC Well 31-1 and Magna Well 44-7. During the second part of the well testing activity, from July to October 1977, several production and interference tests were carried out in the northern part of the anomaly and data was collected from seven wells. Two of the wells, Republic 38-30 and 16–29, were used alternately as production wells. The produced fluids were then reinjected, after suitable treatment, into Republic Well 18–28. The other wells, BUREC 31-1 and Republic 16–30, 56-30 and 78-30 were used as observation wells.

A description of the tests is presented in Table II. All the tests involved variable flow rates. In the case of BUREC tests, flow rates were measured on Well 6-2 by passing the unflashed discharge through an aperture plate and measuring the pressure drop across the plate. In order to measure discharge from BUREC Well 6-1, the fluid was first passed through a steam separator and the liquid phase then passed through a calibrated Weir box. Appropriate corrections for the vapor-phase were made using steam quality estimates corresponding to the temperature and pressure measured at the well-head.