Nevis N-4 Confirmation Drilling Results

摘要

This paper presents the results of the N-4 well drilled on the Hamilton Estate on the island of Nevis, Eastern Caribbean. The N-4 test well was completed with 4-1/2" production casing to a depth of 2,460 feet and open hole to 3,134 feet. Below the clay cap at 2,800 feet lost circulation began to dominate the drilling process and, significant permeability zones were encountered at 2,488 and 2,899 feet. The lost circulation zones appeared to be highly permeable volcanic sands of mixed mineralogy, although limited returns made identification difficult. The well was production tested for 30 hours with wellhead pressure (WHP) steady at 137 psig. The enthalpy of the produced fluids was 459 BTU/lbm. The temperature-pressure logs gathered during testing indicate that at least two production zones were encountered. At the end of the last period of full flow, the sustained production rate from the well was 112 kph (50.8 t/h). Wellbore modeling indicates that a full-size well with 13-3/8" production casing would most-likely produce 526 kph (237 t/h). Fluid chemistry samples collected during production testing of the N-4 well at the Nevis project indicate that the well discharges a mature geothermal fluid that is in equilibrium with temperatures of at least 475℉ (246°C). This is the temperature determined before the onset of the production test. Brine discharged from the N-4 well has a composition that indicates a seawater-dominated reservoir. Reservoir fluids have been characterized as relatively benign and should not present any significant difficulties with production.