Oil

As operator of the Moho-Bilondo field offshore the Republic of the Congo, we are helping to revive production in our long-standing partner country. In addition, by developing "mid-size" deep offshore reservoirs, we are creating new ways to optimize project return.

Maximizing the field's return

Located some 80 kilometers offshore the Republic of the Congo in water depths ranging from 540 to 660 meters, the Moho-Bilondo field is the first of its kind to come on stream in the country. Only two of the four reservoirs discovered, Mobim and Bilondo, covering an area of 72 square kilometers, have been brought on stream so far. Although only a modest amount of oil is produced, the proximity of our offshore and onshore facilities and our experience with deepwater operations help to maximize the field's return.

Heterogeneous reservoirs and different types of oil

Mobim and Bilondo are buried under 1,100 to 1,200 meters of unstable sediment. They were formed about 20 million years ago, when the Congo River disgorged large quantities of sediment rich in organic debris. The sediment spread in successive waves over the deep ocean floor, and the organic matter was gradually transformed into viscous oil. Bilondo's oil is trapped in a series of small sand channels, while Mobim's is contained in two discrete reservoirs. A configuration like this, with discontinuous, composite pockets, is a headache for geologists, who have a hard time predicting how the fluids will circulate during production. In addition, the oil in Mobim and Bilondo is the product of different source rocks, and not equally mature. Bilondo's is seven times more viscous than Mobim's. By using very fine-scale geological models and leveraging our experience in the Gulf of Guinea, we were able to overcome most of these problems.

Made to order

This makes it a little easier to understand what the project's architects, who had to ensure optimal drainage and maximize oil and gas recovery while drilling as few wells as possible, had to deal with. In Bilondo, long, almost horizontal drainholes tap all of the channels. In Mobim, productivity is improved using bottomhole stimulation, in which fractures packed with sand are created. In both cases, to limit subsea infrastructure, the wells were stepped out after the first few hundred meters, despite the sediment's instability. Trajectories were adjusted in real time during drilling, by analyzing the rock being bored.

A rational organization

Various synergies have been achieved between Moho-Bilondo and the Nkossa field, located 18 kilometers away. The water extracted from Nkossa is reinjected into the Bilondo reservoirs, while surplus gas from Mobim and Bilondo is exported to Nkossa. Moored to the bottom by 12 anchors, a floating production unit (FPU) - a sort of factory-barge - handles, receives and processes production. Surplus gas is sent to the Nkossa field for injection and the crude oil is exported to the onshore Djeno terminal. The FPU is connected to the subsea production system by flexible lines insulated from the cold and by control cables known as umbilicals.

Controlled production flows

As always with deepwater developments, cold is a major hazard. Insulation is vital to prevent the crude oil from freezing in the lines. In addition to the techniques we already use in the Gulf of Guinea, insulation solutions known as doghouse, were specially designed to protect the flowline connections. This system makes it possible to shut down production for up to eight hours without hydrate plugs forming in lines, giving technicians the time they need to complete their work.

Bottomhole gas injection

Injecting gas to raise bottomhole pressure and bring fluids up to the surface more effectively is common practice in the oil industry. But the process had never been used before in a deep offshore development. Gas injection has boosted Moho-Bilondo's recovery rate by about 20%. However, the process cools the fluids produced, again creating the risk of a plug in the lines. The amount of gas injected to manage the process must therefore be precisely controlled. Understanding and quantifying the heat exchange phenomena involved were among the most complex challenges we faced in carrying out the project.

Sharing experience

In the Republic of Congo, as in all our host countries, we strive to provide ongoing support for local development initiatives, for example through in-company HIV/AIDS prevention and testing campaigns and funding of treatment, support for local associations to help business startups, and material and financial assistance for institutions of higher education. Moho-Bilondo will contribute to these and other actions. Combining technological expertise, safety and environmental protection, the Moho-Bilondo project and its training programs will also be a vehicle for transferring deep offshore expertise to our Congolese personnel.