Field Development Project 11 – Wells and Facilities Design PDF

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Summary

Running simulations for subsurface wells and surface production facilities for the Wytch Farm Field Development Project....

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Field Development Project 11 – Wells and Facilities Design

Drilling and Production Facilities

Casing and Mud Weight Design Casing and mud weight has been designed based on pore pressure and fracture pressure using RFT data of well 1F-11 where formation gradient was 0.45 psi/ft and fracture gradient was 0.63 psi/ft. However, the gas gradient of 0.1 psi/ft was used for casing design so that it will be set at a depth that prevents formation fracture due to the presence of gas. Casing optimum sizes and details were based on the analogy of offset previously drilled wells. L80 grade was chosen for both casing and tubing as it is usually used in wells with sour environments such as Hydrogen sulfide (H2S) and carbon dioxide (CO2) with economical price and suitable for this reservoir burst pressure. Although PVT data showed no presences of sour gases in the reservoir fluid, it might appear during the waterflooding process, or with high water cut. Optimum mud weight of 10.5 ppg was chosen to ensure that hydrostatic fluid pressure less than fracture pressure and greater than pore pressure in which oil-based mud (OBM) will be used to prevent formation damage due to clay swelling.

Casing design details

Tubing Design

Tubing designed was based on sensitivity using IPR curve to choose the optimum tubing size where the assumptions were 10,000 BOPD for vertical wells and 15,000 BOPD for horizontal wells, as 4.5 inches tubing size has been chosen for vertical reservoir and 5.5 inches for horizontal reservoir to insure maximum flow rate is satisfied with minimum size to be economic and to ensure erosional velocity ratio is less than 0.9.

Tubing size sensitivity analysis for (a) vertical well V2-2, (b) horizontal well H2-5 based on IPR curve

Tubing size sensitivity analysis for (a) vertical well V2-2, (b) horizontal well H2-5 based on Erosional velocity ratio.

Well-Facilities Paths The model was created to account for a 50% water cut at the end of 5 years’ plateau. The figure below shows the map of flowline of 6 inches inner diameter from wellhead to the junction of the well pad, and pipeline of 12 inches inner diameter from the well pad to the gathering centre.

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After running the model, results showed the total flow rate at the separator was 42 MBOPD with a pressure of 200 psi where is supposed to give 100 MBOPD.

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This shortage is due to low flow rates from some wells as a result of pressure losses in the tubing after increasing water-cut.

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Therefore, an Electrical Submersible Pump (ESP), which has a higher efficiency especially for deviated and horizontal wells than gas lift, can be used as an artificial lift method to achieve maximum recovery.

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However, it has some limitation during sand and gas production.

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Since well 1D-02 showed sand production it was decided to install sand screens at the bottom of the wells to limit sand production.

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VFP tables will be imported into the dynamic models to restore the initial production profile.

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After importing the completed layout of the export pipeline, the pressure loss along the export pipeline will be analysed under different pipeline diameters. The optimal diameter will be the smallest one that satisfies the pressure requirement at the terminal.

Well Facilities Path with Pads Details

Process Facilities

Transportation system

Overall, an extensive survey and study were carried out to ensure the proposed facilities locations and pipeline route are not in areas that compromise environmental sensitivity and natural beauty. As shown below, the bulk fluids stream from the Christmas tree of each well from well pad 1 and well pad 2 site is sent via infield flowlines 1.1km and 2.4km long to the common trunk line junction and then via a common flowline 1.2km long to the inlet manifold of the processing facility where crude oil, gas and Liquid Petroleum Gases (LPGs) are separated.

The treated crude oil, gas and LPG export streams are transported by 87km, 84.1km and 84.6km pipelines coated in brown, yellow and grey respectively according to the BS 1710 British Standard Pipe Marking to the Fawley Refinery, N-Power Grid Station, and Flogas LPG station all in Southampton respectively. The facility laying areas and pipeline route were planned to avoid urban centres, natural reserves, environmentally sensitive areas and areas of natural beauty and cathodic protection will be installed for all flowlines and pipelines. The elevation profiles for the export pipelines are shown below and the table gives the summary of the flowlines and pipelines distance and the marker/legend for their locations on the route map.

Summary of flowlines and pipelines route, distance and legend on the map Line

Distance (km)

Water Inj Plant to Well Pad 2

0.67

Water Inj Plant to Well Pad 1

2.7

Well Pad 1 to Common Trunkline

1.1

Well Pad 2 to Common Trunkline

2.4

Common Trunkline to Processing Facility

1.2

Oil Export Pipeline to Fawley Refinery

87

Gas Export Pipeline to N-Power Power Terminal

84.1

LPG Export Pipeline to Flogas LPG Terminal

84.6

Marker

New Forest National Park

Moors Valley Country Park & Forest

Holt Heath National Nature Reserve

Holton Heath Nature Reserve Morden Bog National Nature Reserve

Studland Nature Reserve

Stoborough Heath National Nature Reserve

Hartland Moor National Nature Reserve

Map showing transportation system: major facilities location and export pipelines routes for Oil, Gas &LPG.

Sea Water Injection Treatment Plant Well Pad 2

Well Pad 1

Common Gathering Manifold

Main Processing Station

Map showing transportation system: Well sites and gathering centre location

Elevation profile of treated crude oil export pipeline from processing station to Fawley refinery.

Elevation profile of LPG export pipeline from processing gas plant to Flogas LPG terminal.

Elevation profile of methane gas export pipeline from processing gas plant to N-Power power station....