Planning of Casing Design in AOV-1 Well Drilling, ANTARIS Field KSO Pertamina EP – Banyubang Blora Energi (BBE)

The AOV-1 well is a development well that is planned to be drilled in the “ANTARIS” Field. Based on the data obtained from the nearest well of “AOV-1” well, a casing design will be carried out, therefore it is necessary to select casing specifications. So that it can meet the requirements technically and economically. Casing design planning is the preparation of file collected from drilling prognosis, and daily drilling report so that it can be used for calculation of pressure parameters, knowing stratigraphy, lithology, subsurface data, availability of casing stock in warehouse, and planning technical calculations for casing design operations such as d-exponent calculation to determine pore pressure, pressure calculation (formation pressure, overburden pressure, fracture pressure), calculation of the load received by casing (burst load, burst load design, collapse design), determination of casing setting depth, casing grade selection for casing design, calculation of biaxial stress correction of tension and compression stress, calculation of safety factor, and finally, calculation of economics from planning casing design. 7 ” casing program grade K-55, 20 PPF, BTC at a depth of 0 1968.5 ft TVD with safety factor Ni = 3.83 each; Nc = 2.19; Nj = 13.54, only 1 section is performed. casing program 9/8 " Casing program with grade K-55, 36 PPF, BTC at a depth of 0 820 ft. TVD with a safety factor of each Ni = 9.91; Nc = 4.83; Nj = 30.06, only 1 section is performed. 13 3/8 " casing program with grade K-55, 54.5 PPF, BTC at a depth of 0 250 ft. TVD with a safety factor of each Ni = 63.77; Nc = 22.99; Nj = 226.73, only done 1. The total cost for casing planning is $ 57,689 or around Rp. 816,876,240 of the budget provided, which is $ 65,000 or around Rp. 920,400,000.


INTRODUCTION
After the drilling process reaches the targeted depth, the next step is the casing installation program. The installation of the casing aims to prevent many problems, including the collapse of the drill hole, lost circulation and closing the formation where the formation has abnormal pressure. The grade that the casing will use depends on the depth, formation pressure, formation fracture pressure, and lithology.
Well AOV-1 Field "ANTARIS" owned by KSO Pertamina EP -Banyubang Blora Energi is a development well and the data can still be obtained from the offset well as a sample for calculation. This well penetrates six formations, namely the Lidah formation, Mundu formation, Ledok formation, Wonocolo formation, Bulu formation, and Tawun Ngrayong formation.
The planning process for casing setting depth and casing design on Wells AOV-1. Technically, the casing must be safe, which is able to withstand the loads that will be received on the casing including external pressure, internal pressure and tension load because if the planning is not correct it can cause the casing to break or explode, besides it can cause the casing to break or explode, improper planning can also causing the casing to experience permanent deformation because the tension load on the casing exceeds the minimum yield strength, economically it should be as minimal as possible.
Determination of the casing setting

METHODOLOGY
The methodology in planning the casing design for the well "AOV-1" Field "ANTARIS" includes : 1. Collecting field data that will be needed, such as drilling prognosis, daily drilling report, stratigraphic (formation & lithology), pressure parameters, and stock casing availability data in the warehouse. 2. Planning the operational technical calculations for casing design planning: a. D-exponent calculation to determine Pore Pressure. b. Calculations to determine overburden pressure and fracture pressure. c. Burst load calculation, burst load design, collapse load, collapse load design. d. Determination of the casing setting depth e. Casing grade selections for casing design. f. Calculation of biaxial stress correction of tension and compression stress. g. Economies in casing design planning The following flowchart which can be used to make it easier to understand the methodology that is used in Figure 1.

Filed Overview
The "ANTARIS" Field is included in the working area of KSO Pertamina EP -Banyubang Blora Energy which is located on Jl Raya Cepu Blora KM 5 , Jepon District , Blora Regency . By Geographic wells "AOV-1" which is located in the Field "Antaris" is located in between the coordinate 111o 526 '-111o 123' BT and in between 6o 6o 959'-592 'LS Village Bangoan , District of Jiken , Regency of Blora , Province of Java Central . In regional Fields "AOV" is located 2 km to the west North Northeast Java Basin. Figure  2.

Filed Geology Overview
Geological location of the " ANTRAIS " field is in the Rembang zone , North East Java Basin (Van Bemmelen , 1949). The "ANTARIS" field is located on the anticlinorium hills that extend from West-East.

Well Geology Overview
Based on seismic interpretation, the position of the well "AOV-1" is at the top of the LA layer which is the structural layer of West Banyubang. The LA layer is the target reservoir for oil production, as well as in the entire Banyubang "AOV-1" Well Site Structure (both West Structure and East Structure). Based on the previous report, the results of the Layer Content Test (UKL), the L1 layer produced 346 BOPD, 0.03 MMCFD, and 7 BWPD oil. The other part is in the LC layer which is the oilproducing layer of the East Structure with the Wonocolo Formation carbonate sandstone reservoir. Whereas in the West Structure, the LC layer carried out by UKL at Well 1 is in a different compartment from the West Structure.

Filed General Stratigraphy
In general , Stratigraphy "Antaris" Fields entry into the zone of Rembang follow the scheme are prepared by Pringgoprawiro (1983) can be seen in Figure 4 . Based on the data below the surface of the exploration of hydrocarbons in the region is , units of the stratigraphy of the oldest at the top of the rock base is the formation Kunjung . However, the formation is not exposed on the surface , at the Well AOV-1 Field antaris the target formation is the formation Ngrayong . ( stratigraphic column )  Well Geological Structure "AOV-1" The reference layer in the West Banyubang structure is the LA and LB layers which are the targets of the well "AOV-1", where the layers are oil-producing reservoirs in wells 1 and 3. Whereas in well 4 which is 50 meters from well 1, Layer L1 with a depth down a 7 meter dip filled with water. So it is interpreted that the positions of wells 4 and 1 are close to the WOC. This can also be seen on the depth structure map where the positions of wells 1, 3 and 4 are in the down dip of the west structure anticline.

Determination of Casing Setting Depth
The first plan in well design is the selection of the depth at which the casing is run and cemented . Drilling engineers in depth casing setting planning must consider geological conditions , such as : formation pressure and fracture gradient, hole problems, and other things .
Pressure Formation is the pressure that is caused by fluid in the formation .
Formation pressure can be said to be normal if it has a value of 0.433 psi / ft to 0.465psi / ft. If the gradient value is less than 0.433 psi / Reservoir is a ngerayong formation The petroleum system itself consists of source rock, pressure and temperature, migration, reservoir, caps rock, and reservoir trap.
Source Rock Is a Feather Formation whose lithological characteristics are from the intersection of limestone with calcarenite, sometimes found inserts of clay rock.
Reservoir is a ngerayong formation characterized by the presence of fine-sized quartz sandstones at the bottom and tends to coarse at the top and sometimes limestone.
Caps Rock originates from the Tuban Formation because the formation consists of clay rock and sometimes there are inserts of limestone.
Migration itself is a process of oil and gas moving away from source rock. This process covers a great distance and takes a very long time. ft , the formation pressure can be said to have subnormal pressure and if the gradient value is less than 0.465 psi / ft , the formation pressure can be said to have abnormal pressure . The equation that is often used to determine formation pressure is the dexponent equation (Jordan and Shirley).  The hydrostatic pressure of the drilling mud requires a value greater than the formation pressure.  7) Overburden pressure is the pressure that is generated from the combined weight of the mixture of minerals that precipitated ( matrix rock ) coupled with the weight of the fluid (water, oil , gas) that fills the pores of rocks that .
Generally pressure of overburden will grow large with increasing depth . The normal overburden pressure gradient is 1 psi / ft (0.231 kg / cm2 m). With regards heavy kind of rock an average of 2.3 of a severe type of water, while the magnitude of the gradient pressure of water is 0433 psi / ft, so the magnitude of the gradient pressure of overburden is 2.3 x 0433 psi / ft would be equal to 1.0 psi / ft . In Figure 8 . Shows the EMW pressure window plot between depth vs formation pressure gradient and depth vs formation fracture pressure gradient. In addition, the trip in margin line is also plotted where the value is 0.5 ppg greater than the formation pressure and the trip out margin line which is 0.5 ppg less than the formation fracture pressure. This pressure gradient can be corrected by the provisions of the amount of pressure can be seen in Figure 7 . that Ph> Pf <Prf <Pob.

Figure 8. EMW Pressure Window
Fracturing pressure are pressure hydrostatic formation of the maximum that can be detained without causing the rupture . The magnitude of the fracture pressure gradient is influenced by the amount of overburden pressure , formation pressure and rock strength conditions . Because in fact the overburden pressure gradient is different at each depth .
Can be seen in Figure 9, are requisite conditions of pressure that must be met , namely Ph> Pf <Prf <Pob. If you look at the figure, the pressure has met the requirements, where to determine the casing setting depth you must pay attention to the pressure aspect where the pressure will be received by the casing . lithology and correlation of wells and surrounding stratigraphy. Based on the results of the formation pressure data plot and formation fracture pressure in Figure 10, the depth of the casing settings is obtained from several casings.

Figure 9. Pressure Window Conditions
In this research, the approach method used for determining the casing setting depth is the bottom to top method, as shown in the figure 10. Top (Bourgoyne, Adam T. Jr, dkk., 1986.) The process of determining the length of casing and casing point requires some data, including pressure fracture, pressure formation,   The plot results are used in the process of determining the casing setting depth at Well AOV-1, where the results of the data plot are obtained 3 casing casings. In the calculation process, counting as many as 3 casings, because in this casing depth setting planning using the bottom to top method, the determination of the depth and calculations starting from the lowest casing can be seen in Table 2 . where each casing these are as follows :

Casing Design Planning
In this research, the approach method used for casing design planning is a graphical method, as shown in Figure 14 and Figure 15. The graphical method is used by calculating the load acting on the casing by plotting the pressure against the depth, resulting in burst lines, collapse lines, burst design lines, and collapse design lines. without assuming the worst burden. • Burst pressure design on casing shoe BPD @shoe = Pb @shoe x Safety factor …(14) Plot the Pb @ surface and Pb @ shoe vealue on the chart. The resulting line is Burst load line . And plot the BPD @ surface and BPD @ shoe prices on the graph that has been made. The resulting line is Burst load line design .

Collapse Load
At zero depth or at the surface the   In this research, the approach method used for casing design planning is a graphical method, as shown in Figure 14 and Figure 15. The graphical method is used by calculating the load acting on the casing by plotting the pressure against the depth, resulting in burst lines, collapse lines, burst design lines, and collapse design lines. without assuming the worst burden.  • Cross-sectional area of the casing, in2

Biaxial Stress
• Axial load factor X = (Beban Tension / Pipe body yield strength).. (29) Entering the price of X to the graph baxial stress in Figure 3.12 or already available in Table 6 , so it gained the price factor of collapse strength.
Collapse resistance and Burst resistance corrected to tension loads can be determined by the following equation:     In planning casing also consider aspects of the economy where the grade that has been corresponding requirement is technically required the calculation of the cost of the case in accordance with the prices and supplies are there . Calculation details of the price and the cost of the casing in wells AOV-1 Field Antaris, where the price of casing $ / joint drawn from the data drilling program wells AOV-1.
The total cost of the price of casing $ / joint production 7 "K-55; 20 ppf ; BT; R3 48 ft at Well AOV-1 Intermediate Field for production casing 7 " with a depth of 1968. 5  The total cost of the price of casing $ / joint production 9 5/8 "K-55; 36 ppf ; BT; R3 45 ft at Well AOV-1 Intermediate Field production casing 9 5/8 " with a depth of 820 ft TVD

RESULT AND DISCUSSION
In a process of drilling wells of oil and gas earth for the well development , should no guidelines for carrying out the process of planning it , where the guidelines that can be obtained from wells previously , could also get out of the well closest because they will be there a few factors that must be considered among the factors geology , where the factors of geology encompasses many aspects of which aspects of the stratigraphic layers of a region, area or field it , so it can analyze formations and layers of what course that will penetrate the drilling of stratigraphic that , besides the know lithologic what course are contained in the formation of a layerlasian that , because of the structure of the formation of each region, the region and even the pitch can vary so that in doing correlation to it , to know where the location of the formation of a layer of productive and prospects that will be used as the target of the usual so-called reservoir. The ultimate goal of the well planning process is to facilitate drilling operations where the drilling operation can be completed in a short , safe , efficient and economical operational time in accordance with drilling and production planning .
In the process of casing planning terms of most major before determining casing setting depth is to calculate the parameters required for the process of casing setting depth that the parameters of pressure , there are several parameters of pressure that must be calculated that formation pressure, hydrostatic pressure, overburden pressure and fracture pressure. The requirements that must be met on all parameters of the pressure that is diamana hydrostatic pressure should be great bit of formation pressure, because if the hydrostatic pressure is smaller than formation pressure can lead to problems kick, hydrostatic pressure also should be smaller than the fracture pressure, because if the hydrostatic pressure more large of fracture pressure will lead to the problem of lost circulation, and fracture pressure is smaller than the overburden pressure. If the parameters of the pressure that already meet the rule requirements that apply can be said to suit the requirements and can proceed to the process of casing setting depth planning. Casing setting depth planning can be done by two ways , namely by way top to bottom or bottom to top, the way tesebut used with regard graph of pressure which in the plot that is the pressure formation and pressure fracturing , the thesis is a graph setting depth using Equivalent Mud Weight of pore pressure and fracture pressure. In formations that have pressure window width , will be easy to do approach uses a bottom to top, and if done will get the amount of stretch that is slightly out of the top to bottom. If you have gone through the casing depth setting process so that you know the target depth of each casing , the next step is the casing design planning process .
Casing Planning generally there are two factors that influence is a factor of technical and economic . Will however , Fator technically is a factor that is more preferred than the factor of the economy because if the design of the casing of a well better take into account the factor of economics are more cost sometimes of in terms of technically less meet the requirements and criteria of a safe that will cause problems in later days . There are 3 methods of planning the casing design , namely the graphic method , the maximum load and the analytical method . In the thesis is the method that is used is the method of the graphics , which is a method based on the loads that work on the chassis, by plotting pressure against depth . With steps do the calculations for the parameters of burst load at once make busrt load design, calculation of the parameter collapse load at once make collapse load design, the selection of the chassis that will be used in accordance with the load that has been counted , calculating the load tension and load biaxial to calculate the load that will work on the chassis are the same . After calculating the loads that work on the casing step further is to choose a grade chassis that will be used to protect the well , casing the best are selected is a casing that meets the requirements in the technical and ekonoms . Are technically able to withstand the loads that work on the casing that is internally ressure and external pressure, tension load. In economically , the casing is planned must have cost as minimal as possible The ANTARIS Field AOV-1 well is an onshore development well . Interest does drilling of wells AOV-1 fatherly increase production of oil . Well AOV-1 Field Antaris is a well vertically to a depth of 600 m or around 1968.5 ft TVD, where wells AOV-1 including wells shallow with a target drilling in formations Ngrayong . The well AOV-1 consists of three stretch and one section in each trayeknya , where 3 stretch that is a stretch production, stretch intermediate, stretch conductor. On each casing has a target depth , to stretch production 7 " with the diameter of the hole 8 1/2" has a target with a depth of 0-600 m (0 to 1968.5 ft TVD) and installation of the casing shoe at the depth of the . Casing intermediate 9 5/8 " in diameter hole 12 1/4" having a target with a depth of 0-250 m) (0-820 ft TVD) and installation of the casing shoe at the depth of the . Casing conductor 13 3/8 " in diameter hole 17 1/2" having a target with a depth of 0-30 m (0 to 98.425 ft TVD) and installation of the casing shoe at the depth of the . AOV-1 well planning requires some data such as the parameter data for formation pressure and fracture pressure, mud weight. The data are in the get of Drilling Daily Report (DDR), Prognosis Drilling of wells before and some source other like Mud Logs.
Production casing casing 7 " with a borehole diameter of 8 ½" installed at a depth of 0 -600 m (0 -1968.5 ft TVD) and casing shoe positioned at a depth of 600 m (1968.5 ft), with a mud density of 10, 1 ppg , formation pressure gradient 0.4954 psi / ft and gas pressure gradient 0.0115 psi / ft. The 7 "production casing uses casing grade K-55; 20 ppf ; BTC. The calculation results obtained @surface burst load = 97.28 psi with a burst load design @surface = 1072.811 psi, @shoe burst load = 748.9 psi with a burst load @shoe = 823.79 psi. Collapse @surface load = 0 psi with collapse @surface load design 0 psi, collapse @shoe load = 1033.9 psi with collapse @shoe load design = 1137.2 psi. Results of the calculations are plotted into a graph design casing can be seen in Figure 4.8. Casing with grade K-55; 20 ppf ; BTC has a collapse resistance strength of 2270 psi, internal pressure 3740 psi, joint strength 451000 lbs, pipe body yield strength of 316 000 lbs. By grade casing are on casing 7 " considered in graphic and obtained safety factor respective Ni = 3.83; Nc = 2.19; Nj = 13.54. So that from the results of the calculation of grade casings which have had a power over big of burden who worked on the case and take into consideration of the safety factor also can be inferred grade been able andcan be used for wells AOV-1.
Intermediate casing casing 9 5/8 " with a borehole diameter of 12 1/4" installed at a depth of 0 -250 m (0 -820 ft TVD) and casing shoe positioned at a depth of 250 m (820 ft), with a mud density of 9 , 8 ppg , formation pressure gradient 0.45 psi / ft and a gas pressure gradient of 0.0115 psi / ft. Production casings 9 5/8 " use casing grade K-55; 36 ppf ; BTC. The result of the calculation obtained load burst @surface = 355.15 psi with a design load of burst @surface = 260.85 psi, load burst @shoe = 390.66 psi with a design load of burst @shoe = 286.93 psi. Collapse @surface load = 0 psi with collapse @surface load design 0 psi, collapse @shoe load = 417.87 psi with collapse @shoe load design = 459.66 psi. Results of the calculations are plotted into a graph design casing can be seen in Figure 4.9. Casing with grade K-55; 36 ppf ; BTC has a power collapse resistance is 2020 psi, 3520 psi internal pressure, the joint strength of 755000 lbs, pipe body yield strength of 564 000 lbs. By grade casing are on trajectory 9 5/8 " to be considered as a graphic and obtained safety factor respective Ni = 9.91; Nc = 4.83; Nj = 30.06. So that from the results of the calculation of grade casings which have had a power over big of burden who worked on the case and take into consideration of the safety factor also can be inferred grade been able Jurnal Petro 2021 http://trijurnal.lemlit.trisakti.ac.id/index.php/petro P-ISSN : 1907-0438 E-ISSN : 2614-7297 andcan be used for wells AOV-1.
The conductor trajectory casing is 13 3/8 " with a borehole diameter of 17 1/2" which is installed at a depth of 0 -30 m (0 -98,435 ft TVD) and casing shoe is positioned at a depth of 30 m (98,425 ft), with mud density 9 , 6 ppg , formation pressure gradient of 0.4349 psi / ft and a gas pressure gradient of 0.0115 psi / ft. The conductor casing 13 3/8 " uses the casing grade K-55; 54.5 ppf ; BTC. The result of the calculation obtained load burst @surface = 42.804 psi with a design load of burst @surface = 31.484 psi, load burst @shoe = 47.084 psi with a design load of burst @shoe = 34.633 psi. Collapse @surface load = 0 psi with collapse @surface load design 0 psi, collapse @shoe load = 49.134 psi with collapse @shoe load design = 54.047 psi. Results of the calculations are plotted into a graph design casing can be seen in Figure 4.10. Casing with grade K-55; 54.5 ppf ; BTC has a collapse resistance strength of 1130 psi, internal pressure of 2730 psi, joint strength of 1038000 lbs, pipe body yield strength of 853000 lbs. By grade casing that the trajectory 13 3/8 " to be considered as a graphic and obtained safety factor respective Ni = 63.77; Nc = 22.99; Nj = 226.73. So that from the results of the calculation of grade casings which have had a power over big of burden who worked on the case and take into consideration of the safety factor also can be inferred grade been able andcan be used for wells AOV-1.
The casing cost calculation is based on the casing requirements required in the construction of the AOV-1 Well in the ANTARIS Field . From the results of the calculation of the price of the casing corresponding grade that have obtained the total cost at every trayeknya . On the stretch production obtained a total cost of $ 31 037 or approximately USD 439 483 920, on the stretch intermediate obtained a total cost of $ 23 292 or approximately USD 329 814 720, on the stretch conductor obtained a total cost of $ 3,360 or approximately USD 47.5776 million. So, for the total cost of the whole of elections grade casing for planning the design of the casing wells AOV-1 is $ 57 689 or approximately USD 816 876 240. Values are still below the value of the budget that disedakan is $ 65,000 or approximately USD 920.4 million.

CONCLUSION
After carrying out the technical casing design planning process in the AOV-1 well, several conclusions can be drawn as follows: