Sand Erosion Control by Using Chokes in Series in Deep, High Pressure Oil Producing Wells in North of Monagas, Venezuela

Abstract

Abstract A design of chokes in series has been carried out in order to minimize sand erosion in choke boxes and beams. A multiphase flow simulation program was developed to determine the size of the choke orifices and the sequence of installation. Previous field experience determined beneficial effect of using chokes coated in their internal area from end to end with tungsten carbide. Failures in choke boxes and beams have been occurring in about 59 out of the 222 production strings in the North of Monagas area in Venezuela to the present time. In fact, 139 failures due to sand erosion occurred during 1996 causing repair costs of about $339000. The installation of a design consisting of chokes in series at the well head, drastically minimizes sand erosion, reducing production losses, oil leaks, maintenance costs and unsafe operations. The multiphase flow simulation program based design resulted in the installation of three chokes in series protecting them from sand erosion in the two wells evaluated. During five (5) months, the pre-established period of time for analysis, well No. 1 kept producing continuously. Visual inspection confirmed that no sand erosion had occurred in any of the chokes. Introduction High gas and oil rates associated to sand production with high well head pressures passing through one choke box with conventional material usually causes erosion of the beam and its choke box; the severity of the erosion process may deteriorate them completely, giving place to leaks. Sand production erodes the internal parts of a well head including wing valves, tees, subsurface safety valves, choke boxes and beams affecting the well safety system and production operations. These accessories are inspected periodically, and frequently, they have to be repaired or replaced. This type of failure causes deferred production and dedication of production crews to correct erosion problems affecting operational costs. Research has been carried out on the erosive processes in materials with and without the presence of sand. In the oil industry, an API formula has been developed to predict the limit velocity for flow of fluids, above which an erosive process, in non corrosive environments and without the presence of solid particles, can be initiated. Deffenbaugh showed results on the erosion velocity for carbon steels excluding its application for flow restrictions as chokes. Likewise, Deffenbaugh proposed a formula to predict erosion velocity in the presence of sand. Sontvedt reported the limit velocities for erosion for carbon steels in the absence of corrosive fluids based upon studies of materials for chokes, and also for other special materials resistant to erosion. P. 987^