Hydraulic Fracturing Hot, High Pressure Oil and Gas Wells in Tectonically Active Fields in Eastern Venezuela.

Abstract

The exploitation of the prolific North Monagas reservoirs discovered in 1989 has been hindered by sand production and by asphaltene depositions in the production strings. Wells in these fields have been completed at depths ranging from 14000 to 17000 feet at, original reservoir pressures of 7500–11200 psi. Bottom hale temperatures range from 180 to 307 F and wellhead pressures have reached 7000 psi in the early stages of production. Reservoir fluids have asphaltene concentrations of 5 to 8%, with 200 ppm of H2S and 6 to 10% of CO2. These characteristics of the reservoir and the reservoir fluids represent high risk conditions which have required exercising extreme care in handling the large volumes of crude produced from some 150 active zones. As early as 1991, sand production and asphaltene depositions combined to cause severe well plugging in the Carito Field, making it necessary to start a cleaning program using snubbing units to return production to well potential. In 1994, alter analyzing rock mechanics data acquired in North Monagas, establishing the causes of the sand failure mechanisms and evaluating well production performance under the existing pressure and production rate conditions, it was decided to hydraulically fracture those wells with the most severe sand production problems to improve bottomhole and production tubing flowing conditions. Appropriate hydraulic fracture designs allowed the wells to maintain economically attractive sand free well production rates and higher pressure levels in the system well above bubble point conditions to ensure asphaltene dispersion in the liquid phase and decrease the occurrence of asphaltene plugging. Flow conditions at the flowline wellhead and bottomhole perforation conditions were simulated through the use of commercially available programs versed in nodal analysis.

The work presented herein describes how the application of thermodynamic concepts and the hydraulic fracture programs were used to design and select the high pressure, high temperature treating equipment and fluids programs to control sand production and asphaltene depositions as well as maintain economically attractive oil and gas production rates, thus increasing the physical integrity of the wells.

Introduction

Commercial oil production from the high pressure oil and gas wells in North Monagas was started in 1989 with the perforation and completion of well FUC-1E in El Furrial Field. Results to date have been excellent, having completed wells with production rates up to 8000 BPD. However, sand production and the presence of unstable asphaltenes have hindered the performance of most wells.

The oil producing North Monagas province is an area covering approximately 6600 km2 located some 40 km west of the city of Maturin in the Venezuelan North East (Fig. 1). The area has had 2D and 3D seismic surveys, encompassing the El Furrial, Mulata, Carito, Santa Barbara and Pirital oil producing fields, shon in Fig. 2. Total original volume of oil in place have been estimated at 16.4 MMMBls of liquids and 50600 MMMSCF of gas. The producing fields are of the volumetric type, having found bottom zones isolated by a tar mat which limits any possible aquifer activity.

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