Frontier exploration in the ultra-deep waters of the Congolese offshore.
For Agip Congo and the other oil companies operating in the Congolese offshore, the challenge of the year 2000 is represented by the 2000 meters of water separating the surface from the seabed below which lie big oilfields. These are known as the UDW (ultra deep water) or MTP (Mer Très Profonde) zones.
The first exploration well in the UDW of the Congolese offshore was drilled below 1,900 of water by Total-Fina-Elf, in a block in which Agip Congo is a partner. The water in the block in which Agip is Operator is more than 2000 meters deep.
Field engineers and geologists carry out studies and research in close collaboration with colleagues working in the San Donato Milanese exploration projects unit and other staff traditionally engaged in phases ranging from exploration to production.
Together, on the basis of the prospects already acquired, they collect, compare and evaluate data from different fields and study the scenarios for bringing these fields into development and look for technological solutions for producing oil in situations that were unthinkable until a few years ago.
The deepwater challenge also extends to the drilling sector. Some time ago Saipem drew up an investment plan. Now the new drilling ship Saipem 10000 has set out from the Samsung shipyards in South Korea; the vessel will be able to operate in waters up to 3,000 meters deep.
Interview with Cristiano Salino, Agip Congo exploration manager
What is meant by an ultra-deep water zone?
It is the part of the offshore with a bathymetry ranging from 1,000 to 3,000 meters of water. In the Congolese offshore it has an area of more than 17,000 square kilometers. It is crossed from east to west by the River Congo canyon, its most important physiographic element, which makes an incision more than 600 meters deep in the ocean bed.
The study of the features of the present depositional system of the canyon is providing important information for the modeling of the depositional systems that forged the Tertiary delta of the River Congo, which extends northwards as far as Gabon and southwards to Angola, and within which the oil exploration objectives of this zone are to be found.
These systems have not yet been extensively studied, but have already shown, especially in the nearby Angolan offshore, a very high potential as hydrocarbon exploration themes.
What are Agip Congo’s activities in these areas?
In the Congolese offshore we have big percentages in three of the four existing blocks: Mer Très Profonde Nord, in which we are Operator, with 40 percent; Mer Très Profonde Sud, in which the Operator is Total-Fina-Elf and we hold 30 percent; and Mer Profonde Nord, in which Esso Congo is Operator and we have 30 percent.
These are very big blocks, ranging from 3,500 to more than 5,000 square km. Due to the water depth, the characteristics of the objectives and the scant knowledge available, they are considered of “frontier exploration areas”.
What are the characteristics of exploration in these zones?
They are zones where operating costs are very high, both in the exploration and in the development phase, because of the great water depths and the characteristics of the subsoil. The average cost of a successful well is nearly 30 million dollars.
This is why exploration in these zones employs advanced technologies in continuous evolution and tries to minimize drilling risks and uncertainties regarding the presence and quality of hydrocarbons.
Can you give us some examples of these risks?
First of all, the low temperatures at the bottom of the sea can lead to the formation of gas hydrates which due to their instability constitute a big risk both in the drilling phase and in the testing and production phase.
Also, as they form an impermeable interface just below the sea bed, they tend to trap columns of gas which may endanger the stability of the wells being drilled, given the poor consolidation of the subsoil, which consists of recent soft sediments.
Another problem is the biodegradation by bacteria of the hydrocarbons in the more superficial objectives lying less than 800-100 below the seabed.
These objectives, which have considerable mineral potential, may be affected by biodegradation, the main effect of which is the deterioration of the characteristics of the hydrocarbons present: this may lead to a drastic increase of viscosity, up to levels that may make them impossible to produce.
The phenomenon is still being studied: to be able to foresee its insurgence and entity would enable us to increase considerably the quantities of the producible hydrocarbons we may find in these zones.
What are the “weapons” of exploration?
The main one is 3D seismic surveying, with the support of sedimentological modeling and regional geological studies. Much of the ultra-deep offshore has been covered by 3D surveys.
In the course of the last multi-operator seismic campaign, made in three different permits to create synergies and reduce costs, almost 7,000 sq. km. of seismic representation were acquired.
Thanks to the excellent seismic response generally given by these sediments, it is possible to use non-conventional exploration methodologies, which are employed using the most advanced technologies both in the visualization and in the processing and subsequent interpretation of data.
In this way we can obtain ever more precise information on the subsoil in general and on the petroleum and physical characteristics of the reservoirs in particular.
In particularly favorable situations we can even visualize the presence of the hydrocarbons, thanks to the use of direct hydrocarbon indicators.
This enables us to locate exploration wells with high probabilities of discovery and to make more accurate estimates of the potential reserves than in conventional exploration and to identify fairly reliably those structures that may exceed the minimum economic rates.
In these water depths, the rates must be in the order of hundreds of millions of recoverable barrels.
A great challenge and great commitment?
Certainly - and above all a great opportunity for working in close collaboration with all the units that traditionally come in only in a subsequent stage of the exploration and production process.
The huge investments make it necessary to cut down the time between discovering a field and putting it into production.
This need and the important consequences that the results and decisions taken in the exploration phase may have on a correct approach to the subsequent work of development have made involvement and cooperation indispensable, from the initial exploration phases, of all the units traditionally engaged in the process of exploration, engineering, development and production.