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Enhanced Oil Deliverability Using Simple Technology: Build a Booster Mini Station

Ranov Fasallo, Sumaryanto, I Nyoman Hari Kontha (VICO Indonesia)

Abstract Mutiara-X is an onshore development well drilled on November 2007. It discovered a new oil pool designated the A1 reservoir. The reservoir thickness of this zone is 80 ft with 11 MMstbo of estimated original oil in place. The well is located 7.5 km away from the nearest gathering station in hilly forested terrain. As typical of other Mutiara wells, this well is produced to the gathering station through a flow line. The initial production rate was 1200 bopd with a flowing tubing head pressure of 210 psi. The rate unexpectedly dropped quickly and the flow became intermittent and very sensitive to the pressure changes at the facility's suction header. By time, more frequent flow line gas flushes were required to keep the well on production.

In 2009, a comprehensive study by a multi-disciplinary team recommended an innovative approach to lower the flowing tubing pressure and separately flow between gas and liquid line. This recommendation is to install a booster mini station located close to the well, comprising a separator, a liquid pump, and an additional gas flow line. The project was commissioned in January 2010. As a result, the well rate has now increased to 3200 bopd and is sustaining stable flow. It is estimated that incremental oil reserves of around 400 Mstbo will be achieved. The project has increased VICO Indonesia's total oil production rate by 20%, with very attractive economic result.

This paper will discuss the well performance and value of the project in increasing VICO oil production.

Introduction VICO Indonesia is a production sharing contract operated in the East Kalimantan basin, with wells at Badak, Nilam, Semberah and Mutiara Fields. Mutiara field, shown in Fig. 1, is located in the south of Mahakam River just west of the small town Handil.

Currently Mutiara delivers three quarter of VICOs oil production. These oils come from natural flowing and gas lifted oil wells which are transported into Mutiara gathering stations via flow lines.

Unfortunately, the well head pressure is sometimes not enough to transfer energy to push the oil from well head to gathering station and causes premature abandonment. This is because the reservoir pressure decline naturally along with the production of oil. The condition where Mutiara field lies on hilly topography and the use of single line for multi-phase flow also stir up problem (high friction pressure loss) in transporting oil. Those things were experienced by Mutiara-X where a good oil reservoir, A1, was successfully found and exploited through it.

Reservoir A1 Mutiara-X, located at the Northern part of Mutiara field (see Fig. 2), is a 3-1/2 long string of dual monobore well. Significant oil net pay named A1 was encountered in this well and perforated through shorter string.

Reservoir A1 is a multi-stacking sand with thickness almost 80 ft of net pay sand, 28% of porosity, and 880 mD of permeability. The initial pressure was noted by RFT as 1014 psig.

A1 was firstly produced on March 2008 with initial rate of 1220 bopd and 150 Mscfd of associate gas. Three months afterward, the rate increased to 1640 bopd and 360 Mscfd of associate gas. It was suspected that gas from reservoir A2, which is utilized as in-situ gas lift, increased. The detail production profile is shown in Fig. 8.

PROSPER (NODAL analysis software) was used to estimate the flow rate for several well head pressures and showed that lowering well head pressure could give a higher rate of oil production (see Fig. 3). But in fact, from the beginning of its production, Mutiara- X reactivation by blew the well to atmosphere and flushing the flow line by higher gas pressure was repeatedly executed whenever the well head pressure decreased. Those became more frequent when reservoir pressure started declining.

Lowering the well head pressure could, of course, increase the productivity but the pressure then will not be sufficient to push the liquid to gathering station. A number of 140 160 psig was required to pay delta pressure between Mutiara X and gathering station. With 20 psig of suction separator pressure and flow rate of 1200 1600 bopd, Mutiara Xs well

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head pressure should be around 160 psig 180 psig. This, once again, means that every time the well head pressure dropped to less than 160 psig, Mutiara X would be unable to flow.

Reservoir A1 Reserve There was uncertainty about the original oil in place (OOIP) of A1 since it was developed at Mutiara-X only (limitation of available data). Monte Carlo simulation was, then, used to approximate the value of OOIP.

Figure 4 shows a graphic of cumulative frequency distribution versus OOIP. Based on Archer and Wall3, reserve could be classified as follow:

cumm. freq. reserve classification 10% proven 50% proven + probable 90% proven + probable + possible

A number of 11 MMstb was taken and classified as proven and probable reserve of A1sand. The fact that only 1 MMstb (until January 2010) had been produced from this sand challenge VICO to do some study to enhance the recovery factor.

Surface Facility Development Study In order to lower well head pressure of Mutiara-X and solve the problem in transferring liquid to the station, VICO team recommended three solutions referring to development of surface facility.

Multiphase Pumps The first one was to erect multiphase pumps close to the well as seen in Fig. 5 below:

Application: Heavy oil/low GOR field New oil field development (limited gas facilities) Limited space for Equipment Electricity available

Advantages: Reduce equipment space Able to handle up to 100% GVF

Disadvantages: Need bigger pump & power consumption when

GOR increase over time High customization

Booster Mini-Station To build an oil booster station was another option offered by VICO team. Fig. 6 illustrates the station comprising separator, liquid pump, and new line for

gas. In case of low pressure at the outlet gas, WHC is considered to be tagged to the system.

Application: Applicable for all type of oil field Preferable for high GOR field Applicable for electrical & gas engine

Advantages: Most common used (established technology) No operational issue when GOR increase Able to be operated at FTHP as low as possible

(but need WHC) Low customization

Disadvantages: Need more equipments (flowlines, separator,

WHC), space, and installation cost.

Blow Case Pump The last proposal was to assemble blow case pump (see Fig. 7).

Application: Preferable for remote area and low liquid rate

wells

Advantages: No fuel required No CO2 emission Less equipment compare to multiphase pumps &

booster station Less Maintenance cost Minimum operator involvement.

Disadvantages: High customization Possible need very big space for equipment lay

out

Method Selection High power consumption and big pump size are major issues in VICO so that the option of using multiphase pumps wasnt selected. The use of blow case pumps was more attractive but only when the oil well head pressure close to medium pressure of gas line. Besides, there was lack of information regarding design, similar application in oil industry, and cost estimation.

Booster station (separation, pumps, gas line) was the most recommended method for lowering surface pressure by considering:

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Ability in handling high gas production from high GOR oil wells without any problem.

Availability of gas flowline near to oil wells. Possibility to use idle equipment (pumps and

separator) from other VICO area.

Based on process simulation software (hysis), a number of 65 70 psig is needed at the outlet gas separator to flow gas to the lowest pressure system in gathering station while well head pressure could pay more than 80 psig. Therefore, WHC is no needed to add.

Application Booster Mini-Station, located 1 km away from Mutiara-X, is intended to separate gas from liquid by using two phase separator. Gas outlet from separator is delivered to VLP system while liquid is delivered to oil system in gathering station by using liquid transfer pump. In order to handle liquid condense due to small rate of gas, higher pressure gas from other flowline is injected to gas line outlet separator.

Results Having it set up on January 2010, liquid production from Mutiara-X was diverted from MCP to Booster Mini Station and gave 2500 bopd of the incremental rate. This lowering pressure project also gained more than 2.5 MMscfd of associated gas (see Fig. 9).

Mutiara-Y, which has the same reservoir as Mutiara-X does, also utilizes Booster Mini Station to prevent the inability of reservoir pressure to transport oil to gathering station just because of the same conditions as Mutiara-X had. Until Oct 2010, A1 has been contributing 1.9 MMbbls of cumulative oil.

Conclusion Besides lowering well head pressure of Mutiara-X, Booster Mini Station has solved problem of inability in transporting oil from well into gathering station. This project gave a very good incremental oil rate and able to enhance field deliverabilty. The flow rate became more stable and no more sensitive to pressure changes.

References 1. Rizki, et al., Geological Modeling, fault seal

analysis, and dynamic modeling in E3460 oil reservoir, Dondang area, Mutiara Field, East Kalimantan, Indonesia., IATMI paper, 2010.

2. Permadi, A.K., Diktat Teknik Reservoir I, 2004.

3. Amyx, J.W., et al., Petroleum Reservoir Engi-neering, New York, 1960.

Acknowledgement I would like to deliver honors to the person below who has allowed, supported, and shared information and knowledge in completing and publishing this paper: 1. Bambang Ismanto, VP Resource Management,

VICO Indonesia. 2. Bill Turnbull, Manager of Base Management

Team, VICO Indonesia. 3. I Nyoman Hari Kontha, Pahala Panjaitan, Ade

Lukman, Senior Petroleum Engineering, VICO Indonesia

4. Chrisnadi, Ari Taufiq Kramadibrata, Musyoffi Yahya, Farah Tias, and Nindya Sekar Wiwitan, friends in VICO Indonesia.

Fig. 1 Mutiara Situation Map, red area in left most picture are gas fields, the green one are oil fields, VICO fields are on the onshore of delta Mahakam.

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Fig. 2 Mutiara-X location, represented by blue star. Gathering station location is symbolized by green tringale.

Fig. 3 Inflow vs Outflow diagram of Mutiara-X

Fig. 4 Determination of A1 reserve

Fig. 5 Multiphase Pumps - Simplified Diagram

Fig. 6 Booster Mini Station - Simplified Diagram

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Fig. 7 Blow Case Pumps - Simplified Diagram

Fig. 8 Reservoir A1 production profile

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