Optimization of Horizontal Well Location and Completion to Improve Oil Recovery for an Iraqi Field

Abstract


Introduction
Choosing an appropriate method to enhance production from a mature oil reservoir is a critical decision-making process.A reservoir becomes mature when its production rate decreases after reaching a peak in its production history.This stage of reservoir life is very important due to approaching the profitability limit of the exploitation project (Babadagli, 2005).At this point, new ways to improve oil recovery are needed for such reservoirs (Obaidi et al., 2019;Awadh et al., 2019;Yousef et al., 2020;Ahmed and Al-Jawad, 2020;Al-Al-Obaidi and Al-Jawad, 2020;Al-Mudhafar et al., 2021;Awadh et al., 2021Al-Obaidi et al., 2023;Awadeesian et al., 2019;Roshandel and Siavashi, 2023;Yao et al., 2023).One of the effective ways that has been used is drilling horizontal wells.Horizontal wells have the potential to improve recovery by enlarging the contact area with the oil reservoir and reaching trapped oil formations in the field (Ahmed, 2009;Al-Jawad et al., 2014).Although horizontal wells have many disadvantages, the high investment required for drilling and completion is a stifling factor.Thus, examining the feasibility and features of this method is of utmost importance.Finding the optimal location, length, completion and direction of a horizontal well is crucial before deciding to drill this kind of well and the determination of optimum well placement is a key issue (He et al., 2022;Foroud et al., 2012).The optimization of well placement is a challenging process that is influenced by the fluid properties, reservoir heterogeneity, and the reservoir's development history.However, the objective of well-placement optimization is to optimize the location and orientation parameters of target wells using a reactive control scheme.Reservoir geologists and reservoir engineers commonly develop optimization methods.The integration of seismic, in-situ stress, and gravity data, as well as production data, well log analyses, and well testing data is part of these methods (Humphries and Haynes 2015).The optimum location of the well has a significant impact on the economic income from the exploitation of the oil fields and on the Net Present Value (NPV).Thus, the optimization technique that maximizes oil recovery and the NPV is the most suitable for choosing the right themes and well spacing in the reservoir model (Al-Mudhafar et al., 2023;Al-Rubiay and Al-Fatlawi, 2023).
Well completion is a crucial interface between the productive formation and the wellbore.To complete effectively, it is essential to maintain the mechanical integrity of the borehole without compromising the flow capacity of the well.Optimization of well completions to improve the inflow performance of horizontal wells is a complex, but very practical and challenging problem (Furui et al., 2004;Xiong et al., 2018).From 2006From to 2013, a new open-hole multi-stage completion technology was implemented.The objective of open hole multi-stage system was to improve the efficiency of multistage fracturing, both in terms of time and cost.The wellbore sections were isolated by using hydraulically set mechanical external packers instead of cement.These systems employ Sliding Sleeve Door (SSD) to create ports in between the packers instead of perforating the casing to facilitate fracturing (Casero et al., 2013;Houston et al., 2010;Lohoefer et al., 2010;Seale et al., 2006).
The objective of this study is to perform an integrated evaluation and analysis to optimize the placement, design, and completion of a new directional well; as an oil producer.Oil from the Euphrates reservoir is produced by this new directional well with a completion design of 500 to 700 meters "horizontal section" to secure a high productivity index and increase drainage area, with a target sustained initial production rate of 1-5 Thousand Barrel Oil Per Day (KBOPD).
A horizontal well design with multi-stage completion is studied and proposed to invest and explore optimal oil production in the southeast region of the field.The proposed well path is placed in an optimum way to drain the oil column in the target area with relation to the structure, good reservoir quality, petro-physical properties, and fluid contacts.A "J plan" method is used to start the trajectory kick off at 400 meters from Rotary Table Kelly Bushing (m RTKB) with 89 degrees azimuth, then genteelly build inclination within curve section of 950 meters long till reaching 85 degrees, continue holding along 400 meters section, and then build angle to 90 degrees of maximum dogleg value 2.7 degrees.A bulk oil well sector model is used to simulate the fluid flow of a single-porosity/ singlepermeability model.Simulation sensitivity analysis has been run to optimize; the well trajectory path, different scenarios on well oil and water production potential, and well completion design.To achieve this goal, Petrel RE (Schlumberger, 2019) and ECLIPSE (Schlumberger, 2009) software simulators are utilized.
A is an oil and gas condensate field located in the northeast of Iraq.It is composed structurally of an asymmetric anticline fold; approximately 30 km long and 7 km wide and consists of two domes; the main dome and the north dome; separated by a narrow saddle.Both reservoirs are classified as a gas condensate with oil rim carbonate reservoir.The reservoirs consider one system with good pressure communication due to the existing aquifer.Totally, more than 80 vertical wells are drilled to penetrate the main reservoir of the transition and main pay in the Lower Fars, Jeribe, Dihban, and Euphrates formations (Al-Jabary et al., 2018;Al-Yassery and Al-Zaidy, 2023;Aqrawi, 1998;Jassim, 2006).
The first well, X-01 was drilled in 1977 to penetrate the reservoir at the main dome, but only gas had been discovered; until the drilling of well X-05 at the northwest plunge, in which the test result showed existing of oil.The main challenge of developing "A" field for the production of commercial oil is water and gas production problems; as a result of complex carbonate reservoir features which are caused by tilted oil water contact and withdrawal of gas oil contact.This field is among many structurally oriented NW-SE fields located within the northeastern part of the Zagros Fold-Thrust Belt adjacent to the Low Folded Zone.Fig. 1 illustrates a map displaying the locations of oil and gas fields in northeast Iraq including the studied field (Al-Ameri and Zumberge, 2012;Hakimi et al., 2018a;Mohialdeen and Hakimi, 2016).The stratigraphic column for the studied area including the studied column is shown in Fig.

Well Attributes
The optimal allocation of surface well coordinates was used to invest and explore oil in the southeastern part of the field.In addition, the use of geological and reservoir models allowed us the construction of a smooth well path to penetrate the reservoir target; as shown in Table (1

Well Trajectory, Casing, and Completion Design Path
The actual X-HZ01 trajectory targets the Euphrates Formation, with a Subsurface True Vertical Depth (SSTVD) of -938 m, estimated Oil Water Contact (OWC) in this specific area is: -990 m SSTVD (Deabl et al., 2020).Open hole completion designs are proposed to satisfy the optimum operating condition (flow rate and bottom hole flowing pressure) as follows: • The first section is to be drilled to 400 m RTKB with 17 ½" bit size, cased with 13 3/8'' casing size, and then cemented to the surface.• The second section requires drilling until the 1147 m RTKB (top depth of Jeribe Formation) with 12 ¼" bit size, cased with 9 5/8'' casing size, and then cemented to the surface.• The third section is to be drilled till 1740 m RTKB with 8 ½'' bit size and cased with 7'' casing size and then cemented to the surface.• The fourth section is to be drilled till True Depth (TD) of 2500 m RTKB with 6'' bit size.

Cross Section
The proposed X-HZ01 trajectory targets the formation, with a TVD depth of -938 m SSTVD (estimated OWC in this specific area is: -990 m SSTVD).The proposed trajectory had been designed to start the kick-off point at 400 m RTKB with 89 degrees azimuth at a gentle smooth build inclination of maximum inclination of 90 degrees and dogleg value of 2.7 degrees.Most of the encountered facies are good (in the upper part of the Euphrates Formation in the south), with the majority of dolomitic limestone having slightly better properties.Low and medium porous limestone with only a few strings of expected tight limestone is expected to be below the actual trajectory, but it should not be targeted because it is too close to the estimated OWC (-990 m SSTVD).
The high entry point of X-HZ01 is approximately 350 meters away from the nearest producer (X-05), so there is a low risk of interference.This producer prevents the trajectory from being optimized by shifting the well azimuth to the west (up dip).The proposed well path is placed in an optimum way to drain the oil column in the target area with relation to structure, good reservoir quality, petro-physical properties, and fluid contacts.Fig. (5) shows fluid distribution around well trajectory.

Petro-physical Properties
To ensure optimal well production performance, the well path was directed to penetrate layers having good rock and reservoir properties with 89 degrees azimuth.The properties are; high porous media with an average porosity of 20%, minimum water saturation with a value of less than 15%, and matrix permeability of 50 mD.The studied units contain benthic foraminifera and they are determined based on the presence of the anhydrite, limestone, dolomite, and dolomitic limestone layers (Powers, 1966).Fig. (6) illustrates the rocks and reservoir properties along the proposed well trajectory.

Well Trajectory
The proposed trajectory was designed based on "J plan" method (Joshi, 1992).The kick-off point started at a measured depth equal to 400 m RTKB with 89-degree azimuth, and then gradually increased the inclination within a curve section of 950 meters long until it reached 85 degrees.Continue holding along the 400-meter section, and then build the 90-degree angle of maximum dogleg severity value of 2.7 degrees within a section of 750 meters as shown in Fig. (7) and Table (3).An optimum swellable packer should be selected because it allows water and hydrocarbon reactivation, shorter time for full sealing element reactivation, and has maximum element seal length, and maximum seal diameter.Tubing reamer shoes should be used to avoid any drag and depth off while running the completion.The proposed multistage open-hole completion enables flexibility in isolating undesirable zones (isolated gas breakthrough interval and shutoff water fingering one) by closing the IFCV or SSD that was selected (Dake, 1994).

Well Sector Model
A bulk oil model was used to simulate the fluid flow of single-porosity/single-permeability model (Tarek and McKinney, 2005).A well sector model was generated and run using Petrel RE (Schlumberger, 2019) and ECLIPSE (Schlumberger, 2009)  Simulation sensitivity analysis was run to optimize the well trajectory path, oil and water production potential, and well completion design.Three well trajectories of different Azimuths 89, 104, and 119 degrees were designed; as shown in Fig. (10).The distance from surrounding wells is respected.An 89-degree azimuth was suggested to enter the top of the formation, which is more distant from the gas cap and water leg, in the good dolomitic limestone facies.Results from the well sector simulation model showed that the well trajectory with the 89-degree Azimuth had a slightly better production performance and less water cut; as shown in the simulation plot (Fig. 11), it was used as a base case for the simulation scenarios.By applying constraints on oil and water production, five prediction cases have been simulated using the base case with the well trajectory of 89-degree Azimuth.Table ( 4) presents these cases.The simulation results indicate that the Base Case has a production potential of 20000 STB/day, then sharply drops within two years to an average of 4000 STB/day because of the fast increase of water cut value to around 65%; as shown in Fig. (12).It is concluded that water production constraint should be applied.BaseCase1 shows a production profile for a period of less than six months, the well ceased because of a water cut constraint.BaseCase2 has a shorter production period of less than one year, while BaseCase3 and Base Case 4 have longer production periods of around 4 and 9 years, respectively.It can be concluded that a well production performance can be optimized with minimum production rates of 1000 to 2000 STB/day by delaying and controlling the challenges of producing gas and water.

Conclusions
A horizontal well design with a multi-stage completion is proposed to invest and explore optimal oil production in the southeastern part of the studied field, which is located in the northeast of Iraq.The proposed well path is placed in an optimum way to drain the oil column to the target area with relation to structure, good reservoir quality, petrophysical properties, and fluid contacts.The main conclusions are summarized below.1.A well sector simulation result shows that the well trajectory with an Azimuth of 89 degrees with a multi-stage completion design has better production performance under water production constraints.2. A Base case simulation result shows production potential with a peak of 20000 STB/day, then sharply drops within two years to an average of 4000 STB/day because of the fast increase of water cut value to around 65%.The water production constraint should be applied.3. BaseCase1 simulation result shows a production profile for a period of less than six months, the well ceased because of water cut constraint.

Fig. 1 .
Fig. 1.A map displaying the locations of: (a) Iraqi oil and gas fields; (b) Northeast Iraqi fields including the studied field (modified after Al-Ameri and Zumberge, 2012).

Fig. 2 .
Fig. 2. Part of the stratigraphic column of Iraq including the studied column in the Early-Mid Miocene Sequence (El Diasty et al., 2016).
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Fig. 8 .
Fig. 8. Well completion design consists of lower and upper completion.
software simulators to analyze well trajectory and multistage completion design.Fig. (9) illustrates the boundary of the sector model.

Table 2 .
Planed well path data.