Abstract

After several steamdrive patterns realized in the fractured zones of the Lacq Superieur field, a high rate steam injection in a very low permeability zone through a 350 m horizontal well is presently performed in this field. presently performed in this field. Several tests showed that steam injection through a vertical well was not efficient due to the low permeability. The use of a horizontal steam injection well was, therefore, considered. The combination of steam and horizontal wells is in fact already a reality, in tar sands in Canada for example. The particularities of the Lacq Superieur operation are that the horizontal well is used to have a high steam injectivity in a low permeability carbonated facies and that the drain location is optimized to sweep a large area delimited by existing producing wells.

In this paper, reservoir engineering studies and the drilling of the well are presented. presented. Numerical simulations enabled us:

  • to demonstrate the advantages of ahorizontal injection well with high steaminjection rate,

  • to show the efficiency of the dynamic and thermal mechanisms involved in such a configuration,

  • to optimize the location of the drain between two lines of existing vertical producers with respect to both energy savings and economical aspects.

From the drilling point of view, the geometrical data restricted the drilling domain inside a parallelepiped 9 meters wide by 5 meters high. In addition, a special type of completion was needed to be designed to allow injection in the 350 meters horizontal section only.

The horizontal well was drilled at the end of 1988 and steam injection started in April 1989. In accordance to the guidelines arrived at by numerical simulation, 600 tones per day of steam were injected, without problems. After some changes in the initial conditions of operations, due to a too sharp increase of the flowing temperatures in some wells, the results up to date show clear and promising increases of the oil production in the neighbouring wells. This production in the neighbouring wells. This increase is somewhat earlier than what was predicted by computer simulations. predicted by computer simulations

Introduction

Discovered in 1949, Lacq Superieur field was naturally produced until 1977, the main part of production coming from the fractured parts of the field where oil was swept from the fracture network by aquifer water.

Then steam drive was applied in the fractured areas of the field (ref 1,2 and 3) : in a pilot from 1977 to 1982, in two others patterns in 1983, one of them being still now in operation. The results were good in terms of incremental oil production and OSR. production and OSR. P. 559

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