The Initial Production Strategy

The Volve Oilfield was planned to have a life of about 7 years before attaining an economic limit of 2100 m3/d (13,209 STB/d) oil based on a benchmark oil price of $18.7/barrel. Three production wells, three water injection wells, and production facilities from the Sleipner field were to be used to drain 11.4 Million (71.706 MMSTB) of oil reserves.

Producing Wells

The estimated start date for production was March, 2007 with all producing wells expected to open at a total of around 8000 m3/d and later maintain a plateau production rate of about 9000 m3/d for two years before declining (Image 1). This decline would result only from the water breakthrough. A decrease in water injection intensity is planned to begin in 2011 to keep water production at about 9000 m3/d as oil production continues to decline.

Image 1: Expected oil production rate

Two fluid regions can be delineated, one encountered by the 15/9-19A well and another by the 15/9-19SR well. The initial reservoir pressure of 340 bar (4,930 psi) is not expected to decline up to or below the average oil bubble point pressure of 254.65 bar (3692.4 psi) throughout the life of the field, hence, the reservoir would remain undersaturated.

Table 1: Fluid properties of the two regions defined in the field.

PropertyFluid region AFluid region B
Bubble point pressure (bar)235.5273.8
Viscosity (mPa s)0.790.55
Formation Volume Factor (sm3/m3)1.391.5
Solution gas-oil ratio (sm3/m3)111.8159.1
CO2 (mol %)1.64.9

Solution GOR would remain around 111 m3/m3 and 159 m3/m3 for both fluid regions respectively, and the gas production profile closely resembles the oil production profiles.

Image 2: Expected Gas production rate

The wells were drilled horizontally with a maximum deviation of about 91˚. The trajectory was planned to avoid shallow gas packets and also to allow for better contact with the reservoir. Although flow is expected to occur without need for artificial lift, the oil production wells were completed with gas lift valves in the event of excess water production which could hamper lifting. It requires no sand control because of the well-consolidated reservoir formation.

Encountering shallow gas packets could be hazardous and lead to a blowout while drilling. The best way to prevent this is to not drill in the areas that are suspected to contain them. Hence, if it is suspected that a well is about to encounter a gas packet, the well is deviated in order to bypass it

Injection Wells

The reservoir is expected to have little or no aquifer support (Image 3) and stands a risk of sharp decline in reservoir pressure with continued production. This necessitated the plan for water injection from the onset of production to provide pressure maintenance for the reservoir.

Image 3: The three wells along the structure do not encounter an aquifer

The presence of Barium in the Hugin formation water poses a challenge for the use of seawater to carry out this water injection as the mixture of the barium-rich formation water and seawater could cause the precipitation of Barium and Strontium, potentially harming both downhole and surface equipment. Two water production wells were planned for the provision of injection water, both of which target the Utsira formation.

The water production wells, were completed with electrical submersible pumps (ESP) to allow for an initial injection rate of 16,000 m3/d (100,640 STB/d). Dry wellheads are to be used for all wells, installed just beneath the platform and fitted with a manifold module that can contain up to 13 wells, providing allowance for the drilling of infill wells and/or injection wells later. The Utsira formation possesses loose sands, requiring the installation of sand screens in the water production wells. The maximum deviation angle of the injection wells is 29˚.

Production facility

For oil processing, a jack-up platform with a process module was chosen after which the Navion Saga Warehouse Ship is used as a storage vessel for the processed oil before being ultimately exported via tankers. This processing platform would consist of two 3 phase separators operating at 40 barg (251.6 psig) and 0.2 barg (1.258 psig) with a 5 min retention time.

Retention time is a short period between the inlet and discharge of a volume of reservoir fluid mixture in a separator. This time is designed to allow for the effects of gravity to settle out the heavier fluids, hence, aid the separation process.

The gas is planned to be exported via the Sleipner D sub-sea template to the Sleipner A platform. This reduces the cost of developing new facilities as the platform has already been built and is owned by the same set of companies that own the Volve field. For ease of transportation of the gas, the platform would need to be fitted with a compressor that takes in gas at 40 bar (251.6 psi) and discharges the gas at 100 bar (629 psi).

Image 4: The Production facility setup

Infill Drilling

The Volve FDP looks into various methods for increased oil recovery. The availability of high quantities of gas makes the use of Water Alternating Gas (WAG) injection tempting, but the extra recovery does not offset the extra cost for increased oil recovery. It is for this reason the manifold module was designed with a maximum of 13 wells, giving allowance for extra three oil production wells and two water injection wells.

Also, the completion of wells with gas lift mandrills could improve recovery should the reservoir communication be worse than expected. Shutting down intervals with a high water production rate could also help improve recovery.

Planning for Uncertainties

The major cause of uncertainty in this field is the location of the oil-water contact. The two wells drilled at the initial stages of the project failed to hit a fluid contact. The choice of a fluid contact could significantly increase or reduce the STOOIP and potentially deviate the actual realizations from those planned out. Sensitivity analysis was carried out, and potential contact depths and their probabilities were identified defining best case and worst case scenarios which were then used as upper and lower limit for all the design throughout the development plan.

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7 thoughts on “The Initial Production Strategy”

  1. Hello, how to obtain “image 3”, where to download the related data ?
    I want to get the spatial position (x, y, z) of logs, corresponding to stacked images. But I can not find the related data.

      1. Thank you Ankit for your kind reply! I am trying to find drilling data (like DDR) but not able to access Volve data set, I am not sure if you may share some with me.

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