An oil rim reservoir is a saturated reservoir with an oil column of limited thickness, less than 90 feet, overlain by a gas cap and underlain by an aquifer. Among the various challenges encountered in producing oil rim reservoirs, water and/or gas coning and breakthrough is the most prominent. Water and gas breakthrough occurs majorly due to heel-toe effect and reservoir permeability variations. Inflow control devices (ICDs) were deployed to mitigate the heel-toe effect thereby delaying the water and gas breakthrough.

The reservoir is a typical onshore Niger Delta oil rim reservoir of 30 feet oil column thickness. A long horizontal well of 4250 feet was completed in the oil column. ECLIPSE 100 reservoir simulator was used in modeling the reservoir. To assess the performance of ICDs, two case scenarios were simulated: conventional horizontal well without ICD completion and horizontal well with ICD completion. Modeling of ICDs in ECLIPSE was achieved by the Multi-segment Well model. A multi-segment well model is an advanced well modeling that allows accurate modeling of multi-phase flow and pressure variations in wells with a reservoir simulation model. The well was divided into 25 segments.

This project highlights the benefit of ICDs in mitigating the heel-toe problem faced in oil rim reservoir development. Results obtained from the simulation showed that for the case without ICDs, PLT plot indicated that only about 15% of the well length was contributing to flow. The heel-toe effect resulted in early water and gas coning, and a low oil recovery of 21%. Deployment of ICDs yielded a more uniform fluid inflow (100%) along the entire length of the well; delayed water and gas breakthrough for about one year; increased well productive life by one year; and increased oil recovery by an extra 22% (3.65 MMSTB).











1.0    INTRODUCTION    1

1.1     Background of Study    1

1.2     Statement of Problems    4

1.3     Research Objectives    4

1.4     Significance of Study    5

1.5     Project Scope and Limitations    5



2.1     Oil Rim Reservoirs    6

2.1.1     Oil Rim Development Strategies    7

2.1.2     Technical Challenges of Oil Rim Reservoirs    10

2.2     Oil Rim Reservoir and Horizontal Wells    13

2.2.1     Horizontal Well Completion Techniques    15

2.2.2     Limitations of Horizontal Well in Producing Oil Rim Reservoirs    16

2.3     Application of Intelligent Wells    18

2.4     Inflow Control Devices (ICD)    20

2.4.1     Historical Development    21

2.4.2     Passive Inflow Control Devices (PICDs) Designs    23


3.0    METHODOLOGY    28

3.1     Field description    29

3.2     Modeling approach    32





5.1    Conclusion    42

5.2    Recommendations    43



 Figure 2.1: Types of Thin Oil Column Reservoirs; a) Pancake Shape Thin Oil Column, b) Rim

 Shape Thin Oil Column (Rahim et al., 2013). ..............................................................................    6

 Figure 2.2: Oil Rim Production and Depletion Strategy Screening Guide Line (Olamigoke and Peacock, 2009). ..................    8

 Figure 2.3: Oil Rim Development Terrific Light Screening Guideline (Rahim et al, 2013). ......    9

 Figure 2.4: Coning in (A) Vertical and (B) Horizontal well ......................................................    11

 Figure   2.5:   A)   Schematic   of   a   Vertical   Well Schematic of a Horizontal Well. ......................    14

 Figure 2.6: A Schematic of Various Completion Techniques for Horizontal Wells (Joshi,    1991).............................    16

 Figure 2.7: Water coning due to (A) heel-toe effect, (B) permeability variation. ......................    18

 Figure 2.8: Homogenous formation without ICD (left) and with FloRecTM ICD (right). ........    19

 Figure 2.9: Heterogeneous formation without ICD (left) and with FloRecTM ICD (right). .....    19

 Figure 2.10: Original design of the ICD based on channels of adjustable length (Al-Kelaiwi and Davies, 2007). ..................    22

 Figure 2.11: General ICD fluid flow path ..................................................................................    24

 Figure 2.12: A Hellical Channel-type ICD (Al-Kelaiwi and Davies, 2007). .............................    25

 Figure 2.13: Nozzle-type ICD (Ellis et al., 2010). .....................................................................    26

 Figure 2.14: An Orifice type ICD (Al-Kelaiwi and Davies, 2007). ...........................................    27

 Figure 3.1: Multi-segment well model; green = annulus segment, red = ICD segment, blue -tubin29

 Figure 3.2: Reservoir model showing the oil rim.    30

 Figure 3.3: Water-oil relative permeability curve    31

 Figure 3.4: Gas-oil relative permeability curve    31

 Figure 3.5: Oil inflow profile along the well length without ICDs    34

 Figure 3.6: Water inflow profile along the well length without ICDs    34

 Figure 3.7: Gas inflow profile along the well length without ICDs    35

 Figure 4.1: Cumulative oil production    37

 Figure 4.2: Recovery factor    38

 Figure 4.3: Water cut    39

 Figure 4.4: Gas-oil ratio    39

 Figure 4.5: Oil inflow profile along the well length with ICDs    40

 Figure 4.6: Water inflow profile along the well length with ICDs    41

 Figure 4.7: Gas inflow profile along the well length with ICDs    41


AFI:    Annular Flow Isolator

EOR:    Enhanced Oil Recovery

GOC:    Gas-Oil Contact

GOR:    Gas-Oil Ratio

ICD:    Inflow Control Device

ICV:    Inflow Control Valve

PICD:    Passive Inflow Control Device

PLT:    Production Logging Test

WOC:    Water-Oil Contact



1.1    Background of Study

An oil rim reservoir is a saturated reservoir with an oil column of limited thickness in the order of tens of feet, overlain by a gas cap and underlain by an aquifer. These reservoirs are common throughout the world, and despite their low pay thickness they can still contain substantial volumes of hydrocarbon-in-place (Fajhan and David, 2007). Ezzam et al. (2010) opined that maximizing oil recovery in this type of reservoirs is done by keeping the oil rim in contact with the producing wells at all times which is achievable by balancing the water-oil-contact (WOC) and gas-oil-contact (GOC) movement. For a thin oil rim reservoir with a large gas cap and strong aquifer, achieving the said goal is very challenging (Ezzam et al., 2010; Vijay et al., 1998). Rahim et al. (2013) mentioned water/gas coning and breakthrough, spread out resources, complicated production mechanism, presence of transition and invasion zones, oil smearing, and a low recovery factor of less than 18% as technical challenges of developing oil rim reservoirs.

Among the various challenges of producing oil rim reservoirs, water/gas coning and breakthrough is of utmost consequence. Coning is the mechanism whereby gas or water moves toward the production interval of an oil well in a cone or crestlike manner created by fluid production. It is caused by the pressure drawdown within the oil column close to the wellbore being sufficiently large to overcome viscous and gravity forces and draw the water

or gas into the well. The specific problems of water and gas coning are:

⦁    Costly added water and gas handling

⦁    Gas production from the original or secondary gas cap reduces pressure without obtaining the displacement effects associated with gas drive

⦁    Reduced efficiency of the depletion mechanism

⦁    The water is often corrosive and its disposal costly

⦁    The afflicted well may be abandoned early

⦁    Loss of the total field overall recovery

Delaying the encroachment and production of gas and water are essentially the controlling factors in maximizing the field's ultimate oil recovery.

This problem of water and gas coning is so severe that exploitation of oil rims by means of vertical wells becomes technically and economically infeasible. When a vertical well is drilled through an oil rim reservoir, the length of the reservoir contact in the oil column is small. This low reservoir contact area and the large pressure drop that is associated with flow into a vertical well means that such wells are highly susceptible to coning. Since early 1980's horizontal wells have been used in such situations to defer the water and gas ingress and thus prolong the life of the producer (Vijay and James, 1998). Rahim et al (2013) stated that the use horizontal wells can significantly increase the well contact to the reservoir and can improve the well productivity even up to five times of the vertical wells in the oil rim reservoirs. Thus, the use of horizontal wells has made development of oil rim reservoirs economically viable.

Despite the fact that there are substantial advantages of using a horizontal well over a conventional vertical well in developing an oil rim reservoir, Kabir et al. (2004) stated that placement of horizontal wells in a thin-oil column (< 40 ft) is a challenge and depends on

relative drive indices of the gas cap and the aquifer. Also, -toehe “heeffect”l in h wells, characteristics of the fluids involved, and variations in permeability can result in

unbalanced inflow along the horizontal section and accelerate early water breakthrough and uneven inflow downhole. Hence, horizontal wells are still subject to dual water and gas cresting. In the backdrop of this, research efforts were significantly increased not only to optimize the operations, but also to find supporting technologies to further mitigate the problem of coning in oil rim reservoirs.

To better control the water and gas movement within the limited oil column, horizontal wells with smart well completion (e.g., ICD, ICV, etc.) serves the purpose. Fajhan and David (2007) stated that the employment of intelligent completions in horizontal wells for developing thin oil column reservoirs has already produced many benefits. The application of Inflow Control Device (ICD) is to enhance sweep efficiency and hydrocarbon recovery by suppressing water and gas cones from high rate zones/area created either by heterogeneity or “heel-to-toe effect”in the horizontal wells. This will be achieved by evenly distributing the drawdown pressure along the entire well length and hence both the WOC and GOC move toward the horizontal leg in a more uniform pattern.

This study will investigate the opportunity that intelligent completions (inflow control devices, ICD) provide for efficient oil recovery from thin oil column reservoirs. A dynamic simulation study of an oil rim reservoir in the Niger Delta will be done using a dynamic simulation tool, in an attempt to highlight the benefits of developing an oil rim reservoir using a horizontal well with ICD over a conventional horizontal well without ICD.

1.2    Statement of Problems

Field development teams are always faced with a lot of challenges in the management of thin oil columns due to the fact that the oil reserve is spread out in thin layers with small initial mobile thickness and the presence of huge overlaying gas cap and varying strength of underlying water. This research work will address the early water and gas breakthrough due to “heel-toeeffect”andreservoirheterogeneity associated with producing oil rim reservoirs with conventional horizontal wells.

1.3    Research Objectives

At the course of this work, the extent to which horizontal wells with intelligent well completions affect the performance of oil rim reservoirs will be analyzed. In the light of that, this research will:

1.    Investigate the challenges of thin oil rim reservoirs, reiterate their development strategies and establish understanding of factors that control recovery in oil rim reservoirs.

2.    Carry out flow simulations to predict and compare the performance of oil rim reservoirs under conventional horizontal wells without ICDs and horizontal wells with ICDs.

3.    Mitigate-toetheeffect”“heel   associated   with   co

4    Control water production from relatively high-permeability layers upon water breakthrough.

5.    Maximize production and life of wells.

1.4    Significance of Study

This work will highlight and assess the impact of intelligent well completions –Inflow Control Device (ICD)–in increasing oil recovery from oil rim reservoirs by mitigating the effect of water and gas coning usually associated with developing oil rim reservoirs.

1.5    Project Scope and Limitations

This work is exclusively research based and will therefore, make a study and report findings and discoveries on oil rim reservoir characteristics, challenges and optimization strategies. Inflow Control Devices (ICDs) will be introduced with a concise description of their operating mechanism. A model reservoir simulation will be done, using a dynamic simulation tool. The model is simplified as much as possible with focus on understanding flow dynamics in oil rims to describe an onshore Niger Delta oil rim reservoir. Hence, conclusions and recommendations can be applicable to practical circumstances.




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