MARAVEN has initiated steam stimulation of horizontal wells using two processes: conventional Cyclic Steam Stimulation (CSS) and Single-Well Steam Circulation (SWSC). Horizontal wells typically yield higher primary recovery than vertical wells due to their larger contact area with the reservoir; with the use of steam as both heating and lifting agent, additional recovery is achieved. The well completion designs utilized conventional equipment to minimize costs and to focus efforts on the new stimulation processes with the use of standard completion. Preliminary results for SWCS in the Tia Juana field indicate success as one well has increased its oil production rate by 200 BOPD for one year. The results for CSS in the Bachaquero Field indicate 1000 and 600 BOPD as initial productions.
On the Eastern shore of Lake Maracaibo, five horizontal or highly slanted directional wells (∼70 ° from vertical) have been drilled. The original expectations for primary production performance of these wells has not been realized for at least three reasons: highly oil viscosity, formation damage from the drilling process, and sand accumulation around the liner during early production. Following a long, disappointing period of primary production, it was decided that these wells should be stimulated in two ways: 1)conventional CSS using 5,000 tons of steam, similar to the volume used to treat vertical wells in the area, and 2) SWSC using steam as lifting and heating agent.
Details of the completion design, stimulation, and preliminary results will be given. Results are reported for one SWSC well that has been operational for one year and two wells recently stimulated with CSS.
The ability to increase contact area with the reservoir using horizontal wells has become especially beneficial in areas where heavy crude oil is produced. The use of steam in horizontal wells as a means of displacement has been developed principally in Canada with the outcome being the new technique, "Steam Assisted Gravity Drainage" (SAGD) (Ref. 1, Ref 2). This stimulation method uses two main processes:
steam injection in vertical wells using the horizontal producer at the lower part, and
2) two horizontal wells, one at the upper part to inject steam and the other at the lower part as a drainage point or producer.
This paper discusses three types of steam stimulation in horizontal wells:
single-well SAGD (SW-SAGD), and
steam circulation with production at the same well (SWSC).
Of the five horizontal wells in MARAVEN heavy crude areas, three have been stimulated with CSS and two with SWSC.
Horizontal well stimulation with CSS has apparently found little success, with only a small amount of published information (Ref.3). This lack of success seems due to a lack of accountable incremental production to similar stimulations of vertical wells. Reference 3 cites cases in which a visible production increment does not exist even though the production section is longer.
Numerous economical and technical factors may be blamed for the use of horizontal well CSS.