Summary
The El Furrial field is one of Venezuela's major field assets and is operated by PDVSA (Petroleos de Venezuela, S.A.), the national oil company. Its current production of more than 450,000 BOPD makes it a giant oil field. Development of the field, which has an average reservoir depth of approximately 15,000 ft, is in its mature stages owing to implementation of high-pressure gas injection. PDVSA has consistently followed a forward planning approach related to reservoir management. Using high-angle deviation drilling techniques allows development wells to be strategically located by penetrating the reservoir at high angles to optimize production rate, extend well life, increase reserves per well, reduce operating expenses, and reduce total field development costs.
A reservoir model was constructed and simulated with detailed reservoir stratigraphy to determine realistic potential of high-angle wells (HAW's). Five wells had been drilled as of June 2000, and the first four wells have proved the effectiveness of the design. The philosophy, modeling technique, well design considerations, problems encountered, well results, and economic criteria provide a clear understanding of the risk of this technology not previously used at this depth in Venezuela. The result was the first HAW in the deep, challenging environment of eastern Venezuela.
Results show that optimization objectives can be attained with HAW's, mainly increasing per-well production rate, maximizing per-well recovery, and extending the breakthrough time of gas or water from pressure maintenance and enhanced oil recovery projects. Well results indicate that the geological and simulation modeling technique is reliable and accurate. A pilot program shows that HAW technology provides major advantages to increase production rate and reduce the overall number of wells needed to reach production objectives. However, the project also has experienced a number of unexpected drilling problems.1
The costs associated with the total project are significant, but more importantly, this program becomes very attractive because of the long-term benefits of decreased water-cut related to current water injection; decreased gas breakthrough owing to high-pressure gas injection, and fewer wells required to meet production goals.
Technical contributions include the following:The modeling technique of applying detailed stratigraphy to a full-scale reservoir model is accurate if performed with the appropriate objectives in mind.The application of state-of-the-art drilling techniques to attain high angles at deep drilling depth is possible; however, drilling problems caused by formation instability require more study and experience.This method can be applied to other fields in the eastern Venezuelan basin currently under, or planned to be under, enhanced recovery programs and development programs.
Introduction
The El Furrial field is one of several giant fields found northwest of Maturin, Venezuela, in what is described as the El Furrial thrust trend (location shown in Fig. 1). The field was discovered in 1986 with the FUL-1 well, which established production from the Naricual formation. A late 1996 study, using a full-field simulation model of the El Furrial field, showed that problems associated with gas or water breakthrough in producing wells from high-pressure gas injection and water injection can be reduced with this technology. The potential to reduce problems comes from drilling infill wells at a high angle between the advancing gas and water fronts. High-pressure gas injection was started in 1998 and was justified, in part, by this work and other associated studies. The field produces from two formations, the Naricual and Los Jabillos, giving a total gross thickness of more than 1,500 ft. The primary 1,200-ft-thick Naricual formation is divided into three major stratigraphic sequences - the Superior (upper), Medio (middle), and Inferior (lower). Net-to-gross ratio is typically 80%.
Philosophy
PDVSA has consistently maintained reservoir models through the years to aid in reservoir management.2 To date, eight full-field and numerous sector-simulation models have been built. Optimization of the field began in 1996. During the study, it was noted that predictions of conventional vertical infill wells drilled into the structure had short production lives because of water or gas breakthrough. The review identified the possibility of placing well trajectories between the advancing water and gas fronts. One benefit was that the production rate from new wells could be increased; this indicated that the number of development wells could be reduced, saving investment costs. Thus, the following objectives were determined.Define optimization alternatives of the El Furrial field well-development scheme. The use of nonconventional well completions such as vertical large interval single completions (LISC) and high-angle completion (HAC) wells may present a higher potential for meeting production needs at a lower total development cost.Define the most reasonable completion configuration for new wells in El Furrial field. It is probable that the entire Naricual acts as a single reservoir unit, with at least partial vertical communication existing in the majority of the field caused by fault juxtaposition and limited fractures associated with faults. Therefore, single completions in all of Naricual Superior and Medio, or Naricual Medio and Inferior, may present viable completion alternatives.Provide technical support to the Venezuelan Ministry of Mines and Energy, which approves operation philosophy, development, and completion practices. The HAW program was different from the previous accepted philosophy, so technical support was necessary to permit the FUL-63 pilot test well.
High-Angle Wells
This work was split into two parts. The first was an evaluation of HAC wells as an alternative to current vertical-well strategies. This includes the possible alternative of LISC completions for all of Naricual Superior and Medio. The second was additional simulation cases to test the potential development plan with only HAC wells in a full-scale reservoir model.
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