Successful Experiences for Water and Gas Shutoff Treatments in North Monagas, Venezuela

Abstract

Normally, the average on success rate of water shut-off treatments in the world ranges between 40% - 50%. This average is lower for gas shut-off treatments. In North Monagas, Venezuela, where some hard conditions are present, such as high bottom hole temperatures (over 280 F), in some cases very tight reservoirs which complicates a matrix penetration of any gel treatment without overcoming the fracture gradient, in other cases naturally fractured wells which complicates the effectively fillout of all fracture nets; this success rate could decrease even more, making the treatment not economically attractive. In order to obtain a high success rate in North Monagas, it was designed a special aqueous polymer gel with a low viscosity to handle the difficulty of matrix penetration without overcome the fracture gradient, and delay its crosslinking process for a period of long time due to very low injected rates. Also, it can maintain its blocking properties at temperatures over 290 F without the need to inject cool-down pads; it can perform effectively even gas shut-off treatments, taking into account its difficulty due to higher mobility than water and oil. Carefully studied Coiled Tubing (CT) operations were carried out taking into account the hard conditions already described, without damage other oil producing zones. Several case histories are showed in this paper, including some gas shut-off operations, with the results obtained in each one. As a result, higher water/gas shut-off success rate than the typical average (40% - 50%) was achieved. Introduction Some of the most important reservoirs in Venezuela are located in North Monagas area, which production started in 1988, by PDVSA (Venezuelan National Oil Company). It is placed at Eastern Venezuela (Fig 01). This area is divided in 5 fields called: El Furrial, Orocual, Jusepin, Carito and Pirital. In terms of overall production, El Furrial, Carito and Pirital exhibit the highest production of the area. All presented cases are related to these three fields. North Monagas overall production is about 860,000 BOPD. North Monagas area shows a compositional gradient fluid system that varies from gas condensate to medium oil. Oil API gravity vary with depth from 40 to 16. It is characterized as follows: Wells on this area are completed with cemented casing, and then perforated. Wells flow spontaneously, without any artificial lift method. Production problems are related to asphaltene precipitates and unwanted gas/water production, and in other few cases with sand production. Coiled Tubing (CT) operations are very often in order to maintain production. Well Details Different well completions on this area are described as follows: Wells analyzed in this document are completed with the first two types in the list above (one single production string). Figure 02 shows a typical well schematic from the area. In this case, the well has a 4−1/2″ production tubing and a 5−1/2″ production liner.

Coreflood Testing of Gas-Blocking Agents: Selectivity in High-Heterogeneity Reservoirs and Efficiency in Low-Temperature Conditions

“…The effectiveness of gas blocking of cross-linked polymers or gels have been confirmed in many works, which present experimental and practical applications. , Gels in oilfield conditions have shown the ability to create a strong, long-term gas barrier. During the coreflooding experiments, it was observed that the gel is pumped into the core model with high resistance .…”