TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe
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.
Because of very large reserves of heavy and extra heavy oil, mainly located in Venezuela, the development of technologies for recovering and treating these hydrocarbons becomes a key factor in the strategic valorization of those resources. In accordance with these needs, has been developed since 2005 a technology named INT-MECS®. INT-MECS® technology is a heavy and extra heavy oil deasphalting process for streams coming from waste pits and different production areas; it is based on a liquid - liquid extraction unit, using low molecular weight paraffin solvents under not severe operating conditions (temperature and pressure). INT-MECS® technology has been evaluated at laboratory scale under a batch scheme and finally, using a 250BOPD pilot plant facility, located in Jobo field (Morichal, Venezuela); generating encouraging results with high crude conversion and an improvement in the physicochemical properties of the original fluids coming from PETROMONAGAS upgrader and Morichal's production unit: reduction of viscosities, increase in API gravity (14 – 21 °API deasphalted oils from heavy and extra heavy oils), asphaltene content reduction, desulfurization and demetallization, getting better results in transportation and refining processes. After having passed the stages of laboratory scale and pilot scale tests, this technological solution is currently entering in a visualization study for field deployment in existing upgrading facilities schemes in the Venezuelan oil industry.
Summary The Orinoco Oil Belt in Venezuela contains the largest known deposits of heavy oil in the world, and Cerro Negro is part of the fields in this area. However, the sand production is a major issue which affects the oil production in this field. There are some major issues that stand in the way of the proper cleanout of these wells. These problems include low reservoir pressure, geometry of the wells, and extremely high oil viscosity. Another major problem is the presence of big pieces of progressing cavity pumps (PCP) elastomers, some metallic parts from pressure and temperature sensors configuration, and other metallic parts from previous workover rig operations, encountered during cleanout operations. As a result of these difficulties, some of the past jobs performed in this field were unsuccessful. After these unssuccessful jobs, a campaign of recent multiple sand cleanout jobs was planned in the Cerro Negro field. Numerous difficulties arose during these jobs. These issues were largely due to the presence of big pieces of PCP elastomers and metallic parts. An additional issue was the low reservoir pressure. Due to the size of the casing/liner and the horizontal section, the annulus fluid velocity obtained was insufficient. Therefore, several techniques were applied to overcome these problems. One of these methods was to use reverse circulation for the sand cleanout in the 9-5/8-in. slanted casing section, while circulation was still possible to obtain a higher fluid velocity. Afterward, once the circulation was lost, a special stroking pump was used alongside a large string of tubing to store large amounts of sand and debris. This tool was also used to recover pieces of PCP elastomers and other metallic parts. This tool uses a piston pump to create a vacuum effect, and fluid circulation is not needed for the cleanout. Without this innovative stroking pump, it would have been almost impossible to recover these large pieces. This was the first time this innovative tool was used in these types of wells. When the open horizontal 7-in. production zone was reached, coiled tubing (CT) was used with the proper proportion of diesel and nitrogen to obtain enough fluid velocity and the proper equivalent density. In the end, when necessary, a smaller reliner was run depending on the information obtained during the analysis of the grain sizes. Some techniques were applied to run the reliner successfully in an old and worn out casing, where the geometry of the well and high doglegs caused difficulties. The challenges to complete the cleanout of the well with lost circulation problems included a large annulus area in the highly slanted and horizontal sections, the extremely high oil viscosity, and the presence of large pieces of PCP and metallic parts. These challenges were overcome by using different methods such as the special stroking pump, reverse circulation in the 9.625-in. section, and CT with the proper diesel and nitrogen proportions. Additionally, to keep sand production under control in the cleaned wells, a smaller reliner was run. Finally, these workover jobs were finalized to bring these wells back into production successfully. The oil production results of these operations are shown in this paper, and demonstrated that it is possible to retrieve the production in the sanded wells of the Orinoco Belt in a profitable way.
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