Management of High GOR Wells and Mitigating the Excessive Gas

th
The 8 International Chemical Engineering Congress & Exhibition (IChEC 2014)
Kish, Iran, 24-27 February, 2014
Management of High GOR Wells and Mitigating the Excessive
Gas Production
A. Momeni*, H. Hematpur
Research Institute of Petroleum Industry (RIPI), Tehran, Iran
[email protected]
Abstract
Most of oil fields have limitation of gas handling. A requirement or desire not to flare and the
relatively higher costs of gas compression compared to liquid handling are the main reasons,
considering environmental obligation and surface facilities capacity. Besides, gas production of
primary or secondary gas cap depletes the reservoir energy and reduces its recovery. Scope of
optimization of high GOR wells in gas handling limited fields should result in a higher field oil
rate and should decrease volume of produced gas. This paper recommends empirical observations
and strategy for optimizing high GOR wells in a gas constrained field. These observations and
strategy were practiced in a field and some of the reported results will be presented. In addition to
field scale study, conventional remedies for mitigating the excessive gas production that yield to
increase the GOR will be discussed. At first, the gas entries should be sealed off by gas shut off
techniques. Obviously, the production rate of a gas shut off well decreased and for maintaining the
oil rate, the well performance should be improved. If the proposed techniques were not useful,
then the well structure could be modified to increase oil rims drainage. This means the cost of
drilling or well completion should be regarded. Recent developments in these operations made it
economically acceptable.
Keywords: Reservoir Management, High GOR Wells, GOR Behavior, Production Optimization,
Empirical Observations, Field Strategy, Well Performance.
Introduction
For a field with known production start date, OOIP and OGIP, hydrocarbons production rates,
cumulative production, analysis of the field’s production profile reveals high GOR behavior
of its wells. During the development of the field, the capacity of surface facilities to compress
and process the gas were designed according to predicted production rates of the field, that is,
handling the produced gas has been limited. The field can be named as the gas handling
limited field. If there were not planned to deal with the excessive produced gas, then most
high GOR wells must be shut off. The bulk of petroleum liquids produced from the field with
implemented an EOR scheme is black oil, while the remainder consists of vapor-borne liquids
and enhanced oil [1]. Liquid handling for transferring and sale is relatively more desirable
than gas handling. Also in most cases gas flaring is tightly restricted. Production mechanisms
of such field can be determined. As we know the production mechanism affects the GOR
behavior of the wells. The presented case study is a field that conceptually split into a Gravity
Drainage area (GD) and a water flood area. Since most of the wells in the water flood area
Management of High GOR Wells and …
produced at or near solution GOR, they do not require the optimization [1]. On the other
hand, the wells in the Gravity Drainage area (GD) produce with raised GOR’s and low water
cuts. Because of the restricting factor on production which is volume of produced gas, high
GOR wells of GD of the field were shut-in or chocked back [1]. The wells were divided to
five categories with regard to GOR behavior. Before applying the proposed strategy in the
field, target wells for GOR optimization consist of cycle wells and restricted rate wells [1].
The discussed optimization of high GOR wells is from the field management point of view.
Treatment and remedies for these wells are within a framework and it has a logical guidelines.
It follows economical and operational prinicipal reaesons.
Field identification and definitions
The studied field has numerous wells shut-in due to facility gas constraints [1]. In addition to
gain more oil from high GOR wells, constraint on capacity of gas process faciliteis should be
concerned. Analysising of the wells production behavior demonstrated a complicated problem
[1]. Each well has a unique set of GOR behaviors with respect to chronological time, shut-in
time, producing time and off-take rate [1]. Chronological Time of GOR variation is equivalent
to calculated GOR with respect to time. Over time, a well may exhibit increasing or
decreasing GOR. Shut-in and producing time is defined for a cycling well. When cycling on
and off for a well, the length of shut-in and producing period is shut-in time and producing
time in days respectively. Off-take rate relates to GOR chronological time and it illustrates
corresponding rates. For the GD wells of the field, almost all repeatable long term trends had
been indicated increased GOR with increased off take rate. Similarly, most examined GD
wells display decreased GOR with decreased off-take rate [1]. When a cycle well that had
produced for a while was tested, then choked back and tested immediately, for the second test
often a higher GOR was recorded [1]. Typically the reason for the higher GOR in the second
test is a nearly the same gas rate with a decreased liquid rate. After a period of time, usually
the GOR trend would fall and steady at a lower value [1]. An example of a well’s GOR
behavior is shown in figure 1.
Figure 1: GOR behavior example
th
The 8 International Chemical Engineering Congress & Exhibition (IChEC 2014)
Kish, Iran, 24-27 February, 2014
Ambient temperature changes effect thermodynamic condition for compressors, and therefore
it impacts on gas handling capacity. The range of temperature’s variations is about 120
degrees F annually for the field. Also planned or unexpected equipment shutdowns influenced
gas handling capacity. Thus some wells were brought on and off (producing or shut-in) or
choked back occasionally in order to adjust permitted gas production [1].
In general, the maximum amount of GOR of the field is called Marginal GOR (MGOR). For
each well MGOR could be determined according to the field production data. Base on the
field management, any well with a GOR above MGOR were decided to shut-in. For a
particular well with assessed MGOR, the Net Oil production Benefit (NOB) of the field
calculated as follows [1]:
GOR
NOB = Q × (1 −
)
MGOR
GOR: producing gas oil ratio of a specific well – scf/STB
MGOR: Marginal GOR – scf/STB
Q: oil rate of a specific well – B/D
NOB: Net Oil production Benefit of the field, discounting the excessive gas production of a
specific well – B/D
Principally a strategy for optimizing must prepare a quick response to adapt the subject wells
to facility gas handling capacity
Methodology
In this successful case study, several wells were tested continually as they had produced after
shut-in periods. GOR behavior of the wells were reported and these observations has made it
possible to achieve the prposed strategy . for the field management, special teams were
assigned to monitor and control of the wells production, and consequently they can help to
optimize production from the field. GOR behavior of the wells were examined and it can be
generalized by using defined NOB.
The Strategy that was implied to all gravity drainage (GD) wells of the field, categorized them
to five groups with regard to GOR behavior [1]:
Unrestricted: Relatively low GOR wells that can produce fully open.
Restricted: Near MGOR wells that are the most sensitive to off-take rate. They must produce
at optimum choke setting for maximum NOB.
Cycle: Near MGOR wells that are the most sensitive to shut-in time. Shut-in time, producing
time and off-take rate must be optimized for them.
Swing: Near MGOR wells that are relatively insensitive to shut-in periods or off-take rate.
They can produce or shut, depending on ever varying gas process plant capacity.
Long Term Shut-in: Wells which cannot produce below MGOR.
Results and Discussion
A guideline for remedies and well treatments was offered in the following figure [2,3]. It is
general and for each step, specific method or technique can be suggested [4,5]. NP represents
the net oil production volume in stock tank.
Management of High GOR Wells and …
Figure 2: sequential well treatments guideline concerning technical and economic aspects
Conclusion
A systematic scope to optimize high GOR wells in a gas constrained oil field can yield
increased oil production rate by applying field management skills. Individual well of the
represented field has different GOR behaviors and should be managed with the verified
strategy [1]. The guidline for high GOR well treatments can assist to seek a suitable and
applicable method or technique as a remedy.
Acknowledgement
The authors wish to thank the reservoir studies and field management division of Research
Institute of Petroleum Industry (RIPI) that give us opprotuninty to study about the topic and
search for the available approaches. Thanks are also given to the involved colleagues and
researchers of our division who worked as a team to find an appropriate reply to the project
demand.
References
[1] T. Peruzzi, E. Krumanocker, High GOR Wells Optimization, Prudhoe Bay Practice, SPE
Western Regional Meeting (1999).
[2] D.J. Ligthelm, G.J.M. van Eijden, Gas shut off using foam: The Solution for unwanted
Gas Production, SPE European Petroleum Conference (2000).
[3] J.B. McWilliams, High-Viscosity Crude Squeeze–An Effective Gas Shutoff Technique,
SPE and JPT (1974) 553–555.
[4] A. Frankenburg, D. Hupp, Case Study: Evaluation and Remediation of High-GOR
Horizontal Wells, SPE Annual Technical Conference and Exhibition (2004).
[5] M. Chekani, M.H. Bagherpour, M. Alavi, R. Kharrat, Novel Approach to Mitigate Gas
Production in a High GOR Carbonate Reservoir With Drilled Wells—Case Study, SPE
Production and Operations Conference and Exhibition (2010)

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