Reservoir Characterization of Mid Main Carbonate (MMC) Interval in Cipadati Field (North West Java Basin, Indonesia) to Support Detailed Reservoir Zonation

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  T1S2_O4 Reservoir Characterization of Mid Main Carbonate (MMC) interval in Cipadati Field (North West Java Basin, Indonesia) to Support Detailed Reservoir Zonation _{1 1 1 2 1} Winardi, S. , Toha, B. , Suryono, S.S. , Prasetya, I. ₂ Dept of Geological Eng-UGM, Jl. Grafika No 2, Yogyakarta-55281, Indonesia (winards@yahoo.com) PT. Pertamina EP, Jl. Prof. Dr. Satrio No. 164, Jakarta Selatan-12950, Indonesia

  Generally the MMC is known as a carbonate build up interval in the North West Java Basin, Indonesia, which contains hydrocarbons in some fields such as Rengasdengklok and North Cilamaya. In the Cipadati Field the MMC was drilled by the Explo#1 well and had a thickness of 79 meters. Previously the MMC was assumed to be a homogeneous carbonate reservoir, so petrophysical values gained from the Explo#1 well were used as default values along the entire interval. Further characterization of the MMC is needed to gain a deeper understanding of the heterogeneity of the reservoir including depositional stages, geometry, vertical facies changes, secondary pore types and porosity value. These parameters provided petrophysicists with the information necessary to divide the MMC reservoir into more detailed reservoir zones.

  The most reliable data to characterize the reservoir is core data, however core is non-continuous through the interval so image logs were used as support data in the non-cored intervals. Well calibration was done using image logs, especially in combination with core, thin sections, cuttings and other log data. Lithological texture could be observed within the image logs, so, based on Dunham limestone classification the lithofacies was identified. Seismic facies analysis, supported by well data, was also conducted to reveal the development of carbonate stages and their geometry during the formation of the MMC. The high resolution of the image log tool provided detailed observation of porosity types greater than 2.5 mm. The reservoir zonation was done based on lithofacies, pore types and porosity value.

  The result of characterization shows that MMC is not a continuous single homogeneous carbonate but formed in 12 depositional stages. Externally the geometry of the MMC is of a carbonate buildup (classified as a skeletal mound carbonate), but internally the geometry of each stage varies from mound to sheet drape. Overall the MMC was deposited onto the shelf platform. The MMC in this area does not represent a reef build up. Various lithofacies are found ie alternation between wackstone and packstone in lower part and some shale interruption near the top of the interval. Secondary pore types which are observed along interval are vugular (isolated vugs, interconnected vugs, channeling vugs) and fracture porosity (open fracture and partially mineral filled fracture). The result of porosity calculation shows a variation between 5 and 19 percent. Based on its characteristic the reservoir can be divided into 19 zones (11 reservoir zones and 8 non- reservoir zones).

  Acknowledgements The authors thank to SKK Migas and PT. Pertamina EP for their data support.

  ! " By :

  1

  1

  1

  2 Winardi, S. Toha, B. , Suryono, S.S. , Prasetya, I.

  1 Dept of Geological Eng-UGM, Jl. Grafika No 2, Yogyakarta-55281, Indonesia

  2 PT. Pertamina EP, Jl. Prof. Dr. Satrio No. 164, Jakarta Selatan-12950, Indonesia winards@yahoo.com

September 2013

  

Geological Background

Data & Analysis Result & Discussion Conclusions

  

Geological Background

MMC

  (After TT Jabarut 1998 vide Pertamina, 2005)

  3 BP study team, 1996 EXPLO#1

(Pertamina, 2005)

  MMC in Explo#1 well was assumed to be a single Explo#1 homogeneous reservoir.

  Previously, petrophysic analysis used single/same parameter for whole interval. _{Carbonate build up (eq MMC) distribution in Rengasdengklok high (Pertamina, 2005)} All tested intervals of MMC were water bearing.

  

Data & Analysis

FMI log data from Explo#1 well at MMC interval (1444- 1523 m depth).

  Composite log data (GR, SP , Resistivity, Density Neutron & ).

  Petrophysic analysis from previous study. Cutting description log Conventional core description at 1454.71-1461.3 m depth intervals. side wall core

  14 samples of description. 5 thin section descriptions. 8 seismic lines across Cipadati field. Other wells data around study area.

  5

  Result-1: Reservoir characteristic (Facies, Pore types, Features of subaerial exposure & Depositional stages)

  7 Image display of wackestone and packstone facies. packstone wackestone Image display of Shale and Packstone facies.

  

Distribution of vertical facies unit of MMC in Explo#1

NO. DEPTH (m) THIKCNESS (m) FACIES

  1 1444 - 1455

  11 Wackestone 2 1455 - 1456

  1 Serpih 3 1456 – 1460,3 4,3 Packstone

  4 1460,3 - 1460,7 0,4 Serpih 5 1460,7 - 1462,5 1,8 Packstone

  6 1462,5 - 1462,7 0,2 Serpih 7 1462,7 - 1496.3 33,6 Packstone 8 1496.3 - 1501,8 5,5 Wackestone 9 1501,8 – 1510,5 8,7 Packstone

  10 1510,5 – 1515,3 4,8 Wackestone 11 1515,3 – 1518,5 3,2 Packstone 12 1518,5 - 1523 4,5 Wackestone

  9 Pore Types

Vugular porosity types vug fracture

  11 Feature of subaerial exposure Subaerial exposure example at 1471.3 m

  High GR reading which is caused by the presence of paleosoil (filled secondary pore), as indicator of subaerial exposure.

  4 subaerial exposures are identified along MMC interval, at 1471.3, 1486, 1495, and 1507.8 m depth.

  Depositional Stages & Lateral Distribution

  

13

Result-2: Detailed Reservoir Zonation

  15 POROSITY TYPES 1 1444 - 1453.50

  0.5 Wackestone Interconnected vug 18 1511 - 1515.00

  Vugular & fossilmoldic porosity, use Nugent (1984) Vugular & oomoldic porosity, use Nurmi(1984) Fractures porosity, use Rasmus (1983)

  Log [ф _s ³ + ф _s ² (1– ф _t ) + (ф _t -ф _s )] m = ------------------------------------------ Log ф _t 2(logф _s ) m ≥ --------------- log ф _t

  _s ) m ≥ --------------- log ф _t

  ZONES DEPTH (m) THICKNESS (m) FACIES

  4.0 Wackestone Open/partially healed fracture + vugs 19 1515 - 1523.00 8.0 non-reservoar -

  1.5 Packstone Primer-intergranular 17 1510.5 - 1511.00

  9.5 Wackestone Interconnected vug 2 1453.5 - 1457.00 3.5 non-reservoar - 3 1457 - 1458.00

  1.2 Packstone Interconnected vug 16 1509 - 1510.50

  1.0 Wackestone Partly mineral filled fracture + vugs 14 1499 - 1507.80 8.8 non-reservoar - 15 1507.8 - 1509.00

  0.6 Packstone Partially interconnected vug 12 1495.6 - 1498.00 2.4 non-reservoar - 13 1498 - 1499.00

  7.5 Packstone Channeling vug 10 1493.5 - 1495.00 1.5 non-reservoar - 11 1495 - 1495.60

  8.7 Packstone Interconnected vug 8 1480 - 1486.00 6.0 non-reservoar - 9 1486 - 1493.50

  2.0 Packstone Open fracture + channeling vugs 6 1468 - 1471.30 3.3 non-reservoar - 7 1471.3 - 1480.00

  1.0 Packstone Open fracture + interconnected vugs 4 1458 - 1466.00 8.0 non-reservoar - 5 1466 - 1468.00

Relation between porosity types and cementation factor (m) equations 2(logф

Cementation factor (m) of reservoir zones of MMC in Explo#1

  0.12

  1

  0.19

  0.15

  0.12

  2.28 8 1507.8 - 1509

  1.2

  0.16

  0.08

  0.12

  1.69 9 1509 - 1510.5

  1.5

  0.05

  0.12

  0.09

  1.59 10 1510.5 - 1511

  0.5

  0.17

  0.05

  0.14

  1.31 11 1511 - 1515

  4

  0.21

  0.14

  0.14

  2.04 NO m DEPTH (m) THICKNESS (m)

  2.59 7 1498 - 1499

  17 average average Porosity PhiT PhiE Sonic 1 1444.0 - 1453.5

  9.5

  0.11

  0.27

  0.12

  0.21

  1.46 2 1457 - 1458

  1

  0.37

  0.12

  0.31

  1.90 3 1466 - 1468

  2

  0.24

  0.19

  0.21

  1.71 4 1471.3 - 1480

  8.7

  0.19

  0.12

  0.13

  1.96 5 1486 - 1493.5

  7.5

  0.23

  0.10

  0.18

  1.50 6 1495 - 1495.6

  0.6

  0.19

Re-calculation result of Water Saturation (Sw) of MMC in Explo#1

  0.12

  7

  0.15

  2.28

  4

  0.05

  0.96 8 1507.8 - 1509

  1.2

  0.08

  1.69

  3.5

  0.04

  0.94 9 1509 - 1510.5

  1.5

  0.05

  1.59

  0.06

  0.93 7 1498 - 1499

  0.96 10 1510.5 - 1511

  0.5

  0.05

  1.31

  3

  0.06

  0.99 11 1511 - 1515

  4

  0.14

  2.04

  3

  0.05

  0.95 Rt Sw PhiE Rw m NO DEPTH (m) THICKNESS (m)

  1 1444 - 1453.50

  1

  0.06

  1.46

  0.90 4 1471.3 - 1480

  1.5

  0.07

  9.5

  1

  0.12

  1.90

  2.5

  0.04

  0.97 3 1466 - 1468

  2

  0.11

  1.71

  3.5

  0.07

  8.7

  5

  0.12

  1.96

  4

  0.06

  0.94 5 1486 - 1493.50

  7.5

  0.10

  1.50

  2.5

  0.08

  0.98 6 1495 - 1495.6

  0.6

  0.19

  2.59

  0.99 2 1457 - 1458

  

CONCLUSIONS

1.

  General reservoir characteristic of MMC in Cipadati Field: Consist of some lithofacies of wackestone, packstone and shales.

  Had some subaerial exposures, found at 1471.3, 1486, 1495 and 1507.8 m depth. MMC was formed in12 depositional stages and stage 1, 6, 10, 12 are penetrated by Explo#1 well. Both of intergranular primary porosity and secondary porosity types such as vugular (isolated vugs, interconnected vugs, channeling vugs), fractures (open fracture, partially mineral filled/healed fracture) are observed. Some dual porosity of fractures-vugs system also found.

  (19) different characteristic zones. Eleven (11) zones are reservoir and eight (8) of them are non-reservoir zones.

  19 CONCLUSIONS 3.

  Reservoir petrophysic properties of MMC;

The thickest reservoir is zone 1 at 1444-1453.5 m depth with 9.5 m thick and the

thinnest one is zone 6 at1495-1495.6 m depth with 0.6 m thick. Highest porosity interval is zone 6 at 1495-1495.6 m depth (average PhiE 19 %) and

the lowest porosity interval is zone 9 (1509-1510.5 m depth) and zone 10 (1510.5-

1511 m depth) with average PhiE of both is just 5 %. The highest value of cementaion factor (m) is 2.59 found at packstone facies in zone 6 and the lowest one is 1.31 found at wackestone facies in zone 10. Overall, re-calculation of Sw (water saturation) value in each detailed reservoir zones

using new different cementation factor (m) approach, based on pore types, show

high value of Sw about 93%-99% and this resut is more accurate according to the

well testing result in Explo#1 well that clearly prooved water bearing for all intervals.