multilateral wells in production of thin oil reservoirs dissertation

7/28/2019 Multilateral Wells in Production of Thin Oil Reservoirs Dissertation

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The University of Salford

School of Computing, Science and Engineering

MSc Dissertation Proposal

Name: Fasakin Akinwole Date: 5th Dec, 2012

Proposed Project Title: Production optimisation of thin oil rims, using multilateral

wells.

Brief Outline of the Work:

The most traditional form of wells drilled is the vertical well. Vertical wells are wells

drilled with zero inclination angle. These wells intersect the reservoir bedding plane at

right angles. To further improve upon the performances of these vertical wells

particularly in some areas where vertical wells have not proved to be particularly

successful, significant advances in technology have made it possible to drill horizontally.

By definition, a horizontal well is a well drilled parallel to the reservoir bedding plane i.e.

with an inclination angle of or near to 90 degrees.A multi-lateral well is an advanced form of horizontal well in which there is more than

one horizontal or near horizontal lateral well drilledfrom a single main bore and

connected back to the main bore. This form of wells usually are usually characterised by

complex geometries and architecture. A few of the possible geometries are shown below:

Fig 1. Some possible multilateral well geometries. (Source: Claude Gadele, Grard

Renard, 1999)


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Drilling at inclination angles required for horizontal and multilateral wells (up to 90)

substantially increase the cost of the well but these wells produce certain advantages

which include:

Increased drainage area of the platform, most especially in offshore fields.

Prevention of water and gas coning problems.

Increased penetration of the producing formation.

Improved productivity in fractured reservoirs.

Thin oil rims reservoirs on the other hand, are loosely classified as reservoirs whose pay

zone thickness are in the range of 40ft or less. These reservoirs many times contain

sizable amount of oil that can be recovered and are quite common in many oil provinces

throughout the world where they are often times sandwiched between a gas cap and a

bottom water support.

Maximising recovery from these fields present some challenges, as early water and/or gas

breakthrough leads to uneconomic production from them.

These oil rim fields are of various configurations and depletion strategy must therefore

take into consideration various factors such as their geological configurations, pressure

response to production, etc.

Technical Challenges of exploiting thin oil strata Reservoirs

In thin oil rims sandwiched between gas caps and aquifer support, high

production rates lead to the problem of water or gas coning with the attendant

excessive production of water and gas as compared with oil production.

For reservoirs possessing gas cap/reserve and oil rim, oil is produced first before

gas. This is because if gas is produced first, there will be pressure drawdown and

gas will come out of solution, thereby reducing the amount of oil that can be

produced. Oil migration into upper gas cap zone can also occur with the attendant

oil loss due to saturation in gas.

Also government regulations may be such that with large gas reserves possessing

thin oil rims, maximum production of oil has to precede any gas exploitation. This

present technical challenges of gas coning.


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This dissertation will be looking at economic possibilities of applying the technique of

multilateral wells drilling towards overcoming some of the above highlighted challenges

of producing thin oil rims thus paving the way for a successful economic depletion of

such fields. The possible advantages of this approach in this case include:

A distinct advantage of this drilling approach is reduced costs in comparison with

other comparable techniques like horizontal drilling. This may be explained as a

result of the fact that the cost to drill down and case from the surface to the

productive payzone represent roughly as much as 60% of the total cost of a

conventional horizontal well (which in itself is more economically suited to this

sort of field than vertical wells). The natural corollary of this fact is that for

example, in a thin oil rim field with a large areal extent where it becomes

necessary to employ horizontal drilling for economic production, costs will be

reduced using a single multilateral with 2 or more diametrically opposed branches

or laterals (see Fig. 1 above) rather than employing several horizontal wells for

same areal extent.

Again, very importantly, in situation of thin oil rim reservoirs situated between

gas caps and aquifer support, gas or water coning is usually a problem. In such

circumstances, multilaterals should offer better performance (reduced coning)than horizontal and vertical wells since they permit same rates for larger reservoir

exposure and drainage area, and therefore lesser pressure drawdown on formation.

Also, in situations where the rig size is limited, in the offshore case for instance,

multilateral wells provide the possibility of drilling 2 diametrically opposed wells

in a thin strata reservoir to achieve a large contact area with the reservoir, thereby

eliminating/reducing the need for multiple drilling pads.

This dissertation project shall be more concerned with employing numerical studies

(simulation methods) to undertake the comparison of advantages of applying the

multilateral wells approach to optimisation of production from thin oil rim reservoirs vis

a vis other production techniques, most especially horizontal wells.


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Economic argument

Of the three techniques presently available for drilling oil fields, vertical wells are

practically out of the case for operating these types of fields due to unwanted fluids

coning at any reasonable high production rates. And on the other hand, costs of drilling

enough vertical wells to bring up rates to necessary levels render the project

uneconomical. Employing horizontal wells was able to bring up production rates to

economic levels while suppressing coning problems to sustainable levels and therefore,

horizontal wells have thus sort of become standard industry procedure for operating thin

oil rims for now.

Economic argument for employing multilateral wells in producing these types of fields

stem from the fact that by joining several laterals (horizontal branches) to the same main

bore rising from the top of the reservoir to the surface, the reservoir reach of several

horizontal wells can be achieved while (1) saving costs on having just a single main bore

instead of one for each horizontal well (2) pressure drawdown performance would be

improved/reduced than horizontals as the several laterals can only feed into one main

bore, thus high rate is achieved while pressure drawdown is well restrained.


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multilateral wells in production of thin oil reservoirs dissertation

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