Shreeram Lom, Aaron Rampersad, and Juan Martínez, of Repsol, discuss the Perla field development, which came online offshore Venezuela in July.
Fig. 1: Topside. Images from Repsol.
The Perla field, which is part of the Cardon IV block, is the largest offshore gas discovery to date in Venezuela. The project forms part of the larger Rafael Urdaneta development project, approximately 50km west of the Peninsula de Paraguana (Gulf of Venezuela) in the Cardon IV West concession at roughly 200ft water depth. The field is operated by a company called Cardon IV whose shareholders are Repsol (50%) and Eni (50%). The participation of PDVSA to hold a 35% stake is currently under consideration.
Perla was discovered in 2009 through the exploration well Perla-1X that reached the reservoir at 8780ft true vertical depth subsea (TVDSS). The total original gas in place (OGIP) is 16.73 trillion cubic feet (TCF) and the proven reserves are 9.5 TCF. The production from the field is tied to PDVSA’s pipeline network. The gas sales agreement was signed on 23 December 2012, and the development plan was approved on 20 August 2012.
First gas production started 25 July 2015 with the Perla 7 well producing approximately 135 MMscf/d and 3000 b/d of associated condensate. The full field development will occur in four phases with total estimated investment of US$6.620 million over the life cycle of the project.
Fig. 3: SW-NE seismic line across the Perla Field.
Geology and geophysics
Fig. 2: Structural map of top reservoir.
The Perla field consists of Upper Oligocene to early Miocene carbonates lying on a laterally discontinuous sequence of (Oligocene) siliciclastics, in turn deposited on a basement high. The field is characterized by northeast-southwest trending extensional faults, which are mainly due to the reactivation of the basement faults and also the subsidence caused by the Aruba and Urumaco Troughs. The carbonate is mainly composed by rhodoliths, branching red algae and larger benthic foraminifers with a minor contribution of green algae and corals. In terms of petrophysical properties both core and log data show a general increasing upward reservoir quality trend, with the uppermost unit characterized mainly by primary porosity, whereas the mid-lower units show mainly secondary porosity strongly affected by digenesis.
A 3D seismic acquisition was performed in 2006, which covered approximately 700sq km with a recording depth of eight seconds. The 3D volume is of very good quality showing excellent definition of faults and top carbonate (Fig. 3).
Reservoir and production
Fig. 5: Mudline suspension system assembly diagram.
The Perla 1 reservoir has good petrophysical properties: porosity (15-25%) and permeability (10-80milidarcy (mD) in the upper section) generally degrading downward. The fluid is lean gas condensate (28 stock tank barrels (stb)/MMscf) with a vertical (gravitational) and lateral (origin) variation. The reservoir seems not to be hydraulically compartmentalized.
The development strategy is designed for 21 development horizontal wells, which would be drilled from four offshore platforms. The field development consists of four phases with increasing productions rates of 150 MMscf/d, 450 MMscf/d, 800 MMscf/d and 1200 MMscf/d.
Wells and drilling
Perla development wells are dry surface wells drilled using conventional jackup rigs. The field development strategy also included use of exploration wells as producing wells through tieback. Therefore, the exploration wells were abandoned temporarily using mud line suspensions for future tieback from the installed platforms (Fig 5 and 6). The exploration well campaign commenced in 2009 and lasted until 2011.
The casing design for the Perla field wells in the exploration and development phase consists of the following arrangement:
- 30in conductor casing in a 36in hole
- 20in surface casing in a 26in hole
- 13-3/8in intermediate casing in a 16in hole
- 9-5/8in production casing in a 12-1/4in hole
- 7in production liner in a 8-1/2in hole
In late 2014, a new pre-drill development campaign was started from the same subsea template as two of the previous exploration and appraisal wells. During this stage, two more wells were drilled with large horizontal sections and the wells were again suspended by the use of mudline suspension. After the successful installation of a hub platform, a rig was jacked up and skid placed above the production platform for tieback operations.
Fig 7: Offshore field layout.
The development consists of four conventional four-leg wellhead platforms (Fig 7) operated as normally unmanned installations (NUIs). The platforms are arranged in hub-satellite configuration with three satellite platforms connected to one central hub platform via 14in submarine intra-field flowlines. The production from all four platforms is comingled on the central hub platform and then exported through a 30in, 67 km long submarine export pipeline to an onshore processing plant. At the onshore plant, the production is separated, conditioned and metered. The gas is finally sold through a tie-in to PDVSA’s pipeline network at the connection point called Km 217.
Fig 6: Seadrill’s West Freedom jackup at Perla.
The platform topsides facilities consist mainly of production facilities, utilities and materials handling equipment. No processing is performed on the platforms. As NUIs, the facilities are provided with redundant fiber optic cable (primary) and microwave (secondary) communications. The NUIs are monitored and controlled remotely from an onshore processing plant. To mitigate internal corrosion, the intra-field flowline and platform topsides piping is clad internally with stainless steel.
The development concept was selected and matured through a detailed front-end loading process involving internal and external engineering resources. The first step was a concept screening process, which yielded a broad spectrum of development concepts, which were matured through a pre-front-end engineering design (FEED) process. At the end of the pre-FEED process, the final development concept was selected which was further matured through a FEED process.
The work was executed through an engineering, procurement and construction (EPC) contract through a consortium of contractors. The scope of work for the EPC contractor included detailed design, engineering, procurement, fabrication, transportation and pre-commissioning. A few long lead items were free-issued by Cardon IV. Installation of the platforms was performed through a separate installation contractor. The jackets and topsides were fabricated at an onshore facility in Mexico, transported to the field, and installed using heavy lift vessels. Upon successful completion of the platform installation, the rig was jacked up over the platform to tieback the pre-drilled wells as well as drill the development wells. The final hook-up of the platforms risers with the sub-sea pipelines/flowlines was performed using sub-sea and surface hook-spools. Cardon IV managed commissioning of the offshore facilities and onshore terminal facilities through a commissioning subcontractor.
Shreeram Lom is offshore facilities engineer with 25 years’ experience in offshore oil and gas development projects in several international locations. His current position is offshore engineering manager for Cardon IV Perla project for Repsol.
Aaron Rampersad is a reservoir geophysicist with 10 years’ experience. He worked six years at the TSP asset in Trinidad generating prospects for infill drilling. Currently, he is the development Geophysicist at Cardon IV field for Repsol.
Juan Martínez is a well completion engineer with nine years’ experience, six of them with Repsol assigned to Cardon IV since Perla Field exploration campaign in January 2010.