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Collaborating Authors
Pena, Alejandro Andres
Overcoming Excessive Fluid Loss in Tip-Screen-Out Stimulations of Depleted, High-Permeability Reservoirs Using a New-Generation Viscoelastic Fluid: Successful Case Histories in West Venezuela
Parra, Pablo Alejandro (Schlumberger) | Miquilena, Emilio (Schlumberger Well Services) | Sanchez, Alfredo Eduardo (Schlumberger) | Pena, Alejandro Andres (Schlumberger) | Garcia, Argenis Gerardo (PDVSA INTEVEP) | Millan, Mavis Del Pilar
Abstract Tip-Screen-Out (TSO) stimulations of high permeability reservoirs have been performed in North and South America (i.e., USA, Venezuela, Trinidad, Colombia), in Africa (i.e., Nigeria, Gabon, Congo, Ivory Coast, Cameroon), in Europe (i.e., North Sea, Italy), in the Middle East (i.e., Saudi Arabia) and in Asia (i.e., Indonesia). As reservoirs in these regions mature, fluid loss control and fluid-inflicted formation damage become increasingly important and conflicting issues. On one hand, the use of classic fluid loss additives and/or fluids with good fluid loss control characteristics (i.e., polymer-based fluids) is typically associated with well production impairment because of residues left in the formation. On the other hand, fluids that are considered nondamaging, such as viscoelastic surfactant (VES) fluid systems, typically exhibit limited fluid loss control capabilities, making fluid efficiencies low and proppant placement inadequate. Nondamaging fluids are needed that can deliver adequate fluid loss control under severe reservoir conditions (i.e., upon concomitant occurrence of high permeabilities and low reservoir pressures). Bachaquero field located in Lake Maracaibo, Venezuela, and managed by Petróleos de Venezuela (PDVSA) is a critical example of these depleted, high-permeability reservoirs. Permeabilities in this field range from 100 mD to 1 D. The average pressure gradient is 0.2 psi/ft. VES fluids typically have been used to hydraulically fracture reservoirs in this field. However, fluid efficiencies observed in recent jobs were as low as 2% and proper proppant placement under these conditions was no longer possible. In our study, we consider relevant technical aspects and case histories in a systematic study that is aimed at assessing the usefulness of a new-generation VES fluid tailored for high-permeability reservoirs to address low fluid efficiencies in the Bachaquero field. The study encompassed adjustments in fluid formulation to ensure compatibility with local production water and crude oils, specific engineering and quality assurance/quality control guidelines, and field trials in 10 wells, followed by quantification of the enhancements achieved in fluid efficiency and well production. Field tests showed that fluid efficiencies increased by up to 325%, as compared to conventional VES fluids previously used in this field. Production expectations were exceeded in all tested wells by an average of 65%. The study concluded that the new-generation VES fluid is suitable for use in the Lake Maracaibo area and it has been adopted as the fluid of choice for Bachaquero field. What we learned from this successful campaign is valuable when assessing stimulation strategies for mature high-permeability reservoirs worldwide. Introduction Bachaquero field is located on the Eastern side of Lake Maracaibo, Venezuela. It is operated by Petróleos de Venezuela (PDVSA). The majority of the field is located on the lake's shore and the reservoirs that are being stimulated belong to unconsolidated Miocene formations. Permeabilities in the area are high, ranging from ca. 100 mD to 1 D. These are depleted reservoirs, with an average pressure gradient of 0.2 psi/ft and depths ranging from 2500 ft to 6000 ft. Bottomhole temperatures are between 120°F and 150°F.
- South America > Venezuela > Zulian Region > Lake Maracaibo (0.87)
- South America > Venezuela > Zulia > Maracaibo (0.66)
- Energy > Oil & Gas > Upstream (1.00)
- Government > Regional Government > South America Government > Venezuela Government (0.97)
Optimal Practices to Remediate and Control Fines Migration in Inland-Water Wells in the Maracaibo Basin, West Venezuela
Chavez, Nelson (Petroleos de Venezuela S.A.) | Colmenares, Oscar (PDVSA) | Pena, Alejandro Andres (Schlumberger) | Fuenmayor, Argenis (Schlumberger) | de Sousa, Virgilio (Schlumberger) | Miquilena, Emilio (Schlumberger Well Services) | Maiz, Oscar (Schlumberger Well Services) | Escobar, Juan Carlos (Schlumberger Well Services)
Abstract This paper summarizes the following aspects of a comprehensive program intended to develop optimal practices for the stimulation of wells in the Ceuta field, a developing area located in Lake Maracaibo, West Venezuela: lab testing to diagnose formation damage mechanisms and to qualify proposed treatments; operational practices including injection sequence, treating volumes for optimal radial penetration and diversion techniques for uniform placement; recommended safety and environmental practices. Also, detailed examples of treatments performed in six inland-water wells in the Ceuta, Area 8 South Central area within this field are provided. The average production rate for these wells before the implementation of these practices was 419 BOPD. The implementation of the guidelines provided in this paper resulted in an average post-production rate of 2100 BOPD with a twelve-month average decline rate of 1.6 BOPD. The enhanced methodology has been implemented with success in other fields in the Maracaibo Lake area known as CentroLago, Lagotreco and Lagocinco. Results from treatments in these areas are also summarized and discussed. Introduction The Ceuta Field is a developing oilfield located in the Maracaibo Lake area, West Venezuela (see Figure 1). Hydrocarbons of ca. 20–37 º API are produced in this field from sandstone layers with permeabilities ranging between 25–115 mD in a gross interval of approximately 700 feet that includes the reservoir units commonly referred to in the Maracaibo Basin as units Misoa B 3.4 to B 6.0. Bottomhole temperatures range between 290–310 ºF and reservoir pressures range between 4000–6500 psi with depths of about 16,500 ft. The stimulation of wells in this field is a challenging task from technical and operational standpoints due to the diversity of formation damage mechanisms (chiefly fines migration, with deposition of clays, organic compounds and scales also occurring), bottomhole temperatures and large pressure gradients between producing sandstone layers. The purpose of this paper is to report recent innovations in the matrix stimulation strategy for the Ceuta field that have resulted in improved production results over previously reported stimulation protocols. Specifics regarding typical fluid formulations, operational practices for injection sequence, treating volumes for optimal radial penetration, diversion techniques for uniform placement and recommended safety and environmental practices are described and discussed. The recommended stimulation protocol, with is referred within PDVSA as "Liquid HF", has been successfully implemented in other fields in the Maracaibo Lake area Centro Sur Lago, Lagotreco and Lagocinco. Results from stimulation jobs in these fields with the Liquid HF protocol are also summarized and briefly reviewed. Near-wellbore Damage Mechanisms Laboratory studies performed on crude oil and core samples from the areas of interest allow determining the prevailing mechanisms that impair well production. A previous study 1 determined that fines migration is a key impairing near-wellbore area for the Ceuta field. This assessment was achieved via mineralogical analyses by means of X-ray diffraction, flow tests on representative cores from the field and scanning electron microscopy. These studies concluded that there are clay particles, specifically kaolinite and smectite/illite ("mixed layer"), that can be dispersed with relative ease and migrate with fluid flow to further deposit in the pore throats, thus reducing the effective permeability of the porous media.
- Geology > Mineral > Silicate > Phyllosilicate (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.55)
- South America > Venezuela > Zulia > Lake Maracaibo > Maracaibo Basin > Ayacucho Blocks > Bachaquero Field (0.99)
- South America > Venezuela > Trujillo > Maracaibo Basin > Ayacucho Blocks > Ceuta-Tomoporo Field (0.99)
- North America > United States > California > Sacramento Basin > 3 Formation (0.99)
- South America > Venezuela > Lake Maracaibo > Maracaibo Basin > Lago Field (0.98)
Abstract Frac-pack is a pervasively used completion technique in wells targeting high permeability, poorly consolidated and depleted sandstone formations located in Bachaquero, TÍa Juana and Lagunillas fields in West Venezuela. This technique combines stimulation and sand production control in a single treatment by placing a short and wide fracture which bypasses the near-wellbore damage, while gravel-packing the zone of interest. This paper describes a novel and economical frac-and-pack technique which consists of pumping a sand plug with the downhole tool set for circulation to isolate a bottom set of perforations, followed by conventional frac-and-pack. When this procedure is followed, the fracture is forced to propagate along the upper intervals. This novel technique is particularly useful for wells with water-producing zones near the bottom of the target zone, because it induces selective growth of the fracture along the upper intervals and mitigates the risk of growing the fracture into the water-producing zone. A case study of a frac-and-pack performed in a Lagunillas field well with a water contact 40 ft below the target zone is reviewed. The intervention rendered an increase in well production rate from 27 to 173 net barrels per day with a reduction in water cut from 25% to 9%. In contrast, two wells in the same field and with very similar characteristics which were frac-and-packed conventionally rendered 100% and 63% water cuts, respectively. Another application of this technique refers to frac-and-pack of wells with long perforated intervals where early wellbore screen-out may occur due to proppant bridging of the annular volume between the screen and the casing. Conventional frac-and-pack of twenty wells in these fields with perforated intervals exceeding 90 ft rendered a 40% early wellbore screen-out rate. The early wellbore screen-out rate was reduced to 12% in a sample of twenty eight wells with the new technique. The average production rate increased from 2 to 135 BOPD, whereas the average estimated after-treatment production was 130 BOPD, for which this technique was considered successful. A shortcoming of the technique for this application is the fact that the bottom of the perforated interval is not fractured. High-end frac pack techniques that overcome this issue such as use of shunt tubes were found to render higher normalized oil production rates. Introduction Frac-and-pack was first implemented in Venezuela in the early 1960s 1. Small scale stimulations were performed using crude oil as fracturing fluid with gravel sized to control production of formation sand. Ball sealers were used in long perforated intervals as diversion mechanism to achieve better zone coverage. After the treatment was performed, a screen was washed down through the gravel remaining in the casing and additional sand was placed around the screen. Frac-and-pack became a premier completion technique in the late 1980s 2 when the use of the tip-screenout (TSO) technique earned worldwide acceptance as an effective stimulation method for high permeability formations. Modern frac-and-packs involving the use of the TSO technique, high proppant concentrations and gelled fracturing fluids were first introduced in Venezuela by Schlumberger in 1996. Since then, this technique has become the preferred option to stimulate unconsolidated sandstones with low reservoir pressures. Currently, 40% of stimulations performed in unconsolidated sandstones for Petroleos de Venezuela S.A. (PDVSA) in West Venezuela are frac-and-packs. The importance of the frac-and-pack technique relies on the fact that less rig time is required with respect to a job for which stimulation and gravel packing are performed in separate stages. Therefore, the client cost for the workover operation is significantly reduced. Frac-and-pack also eliminates the risk of damaging the near-wellbore properties of the fracture with well cleanout operations required after fracturing and before gravel packing, when both are performed separately.
- South America > Venezuela > Zulian Region (0.54)
- North America > United States > Texas > Dawson County (0.24)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.94)
- Geology > Geological Subdiscipline > Geomechanics (0.65)
- Energy > Oil & Gas > Upstream (1.00)
- Government > Regional Government > South America Government > Venezuela Government (0.55)
- South America > Venezuela > Zulia > Maracaibo Basin > Ayacucho Blocks > Lagunillas Field (0.94)
- South America > Venezuela > Zulia > Lake Maracaibo > Maracaibo Basin > Ayacucho Blocks > Bachaquero Field (0.94)
- Well Completion > Sand Control > Frac and pack (1.00)
- Well Completion > Hydraulic Fracturing (1.00)