PA96
-
1.1-
073PROCEEDINGS, INDONESIAN PETROLEUM ASSOCIATION Twenty-First Silver Anniversary Convention, October 1996
TARAKAN SUB-BASIN GROWTH FAULTS, NORTH-EAST KALIMANTAN: THEIR ROLES
IN
HYDROCARBON ENTRAPMENT
Elan Biantom"
M. Indm Kusuma*
Lindy F. Rotinsulu*
ABSTRACT
The Tarakan sub-basin is one of several sub-basins located in the northeast Kalimantan Basin. This sub- basin is located between the Tidung sub-basin to the north and the Berau sub-basin to the south. To the west, the Tarakan basin is bordered by Sekatak Ridge, and to the east by the present day deep water area of the Makassar Strait.
Geologically, the Tarakan sub-basin is subdivided into 5 geological provinces : (1) Daino-Sebuku Platform, (2) Sem bakung -B ang kudulis Graben, ( 3 ) D asin-Fanny Ridge, (4) Mintut-Tibi Slope, and ( 5 ) Bunyu-Tarakan Main Depocenter. Tectonically, these provinces are separated by normal faults controlled by Oligocene to Pliocene growth fault systems. 3 5 exploration wells have been drilled in the sub-basin, with only nine discoveries. The discovery wells are located in Sembakung-Bangkudulis Graben, Mintut-Tibi Slope, and Bunyu-Tarakan Main Depocenter.
Fault development occurred during three periods: Late Oligocene-Early Miocene rift faulting, Middle-Late Miocene growth faulting, and Mio-Pliocene growth faulting. The Middle-Late Miocene faults are rejuvenation of previous faults, coinciding with a change in sedimentary pattern from transgression to regression. Hydrocarbons were trapped by the Middle-Late Miocene and Mio-Pliocene growth faults.
The geometry of structural traps are described as four way dip, roll-over against fault, fault traps, and unconformity closures.
* Pertamina
An evaluation of the faulting mechanism concluded that structural traps formed by faults depend on their sealinghon-sealing condition, distance from the kitchen area, timing of migration, and the age of the faults themselves. The faults could be acting as migration path-way or seal. This paper tries to investigate and display the relationship between faults and hydrocarbon accumulations, and to predict which closures have a high probability of being traps.
INTRODUCTION
The Tarakan sub-basin is one of several sub-basins located in the NE Kalimantan basin in the north- eastern part of Kalimantan (Figure 1). It lies between the Tidung sub-basin to the north and the Berau and Muara sub-basins in the south. To the west the sub- basins are bounded by the Sekatak Ridge and to the east they open towards the Makassar Strait where deposition still occurs. The Muara sub-basin, at the southern-most part of the Tarakan Basin, lies directly next to Mangkalihat Ridge.
Hydrocarbon exploration activities in the Tarakan sub- basin have been quite intensive, especially during the 1970s and 1980s. At least 3 5 exploratory wells have been drilled, but only 9 were discoveries. Of the 4 producing fields from those decades, there are 3 fields still producing: Tarakan Field, Bunyu-Tapa Field, and Sembakung Field. The Bangkudulis field stopped production in 1988.
Considering the high risk of failure, it seems that the main obstacle for hydrocarbon exploration is the complex geology of the area. This paper attempts to discuss the structural aspects which may influence hydrocarbon entrapment in the Tarakan sub-basin.
Contents
Search
Tectonic Setting
The development of the structures in the Tarakan sub- basin occurred in several stages which to a large extent control the sediments deposited in the area.
The structural configuration was initiated with rifting (Early Eocene), causing the development of block- faulted horsts and grabens (Figure 2). The grabens contain the oldest sediments in the sub-basin, the Middle Eocene Sembakung Formation. This formation consists of strongly compacted shale and silt. Because the pre-Tertiary sediments have not been penetrated in any wells nor have they been detected from seismic data, the Sembakung Formation is considered as the economic basement in the Tarakan Basin.
The rifting process was in part contemporaneous with uplifts in the western part of the sub-basin that controlled the sediment cycles deposited in the Tarakan sub-basin. The Middle Eocene uplift caused erosion of the crest of the Sekatak High and started the deposition of sediments of the first cycle (Cycle- 1) : Sujau Formation, Mangkabua Formation, and Seilor Formation. These formations lie unconformably on top of the Sembakung formation and were deposited in a littoral to shallow marine environment.
Cycle-2 deposition began with the Early Oligocene uplift and consisted of the Tempilan and Naintupo formations which lie unconformably on Cycle-1 . Generally, sediments of the 2 cycles were deposited during the transgressive phase. This changed to regressive when the rifting and uplifting processes reached the peak at the end of Early Miocene.
Distinctly different from previous uplifts that occur only in the western part, this last uplift also extended to the east, forming the Dasin-Fanny Ridge. This rifting and uplifting event formed normal faults trending southwest-northeast and a new basement configuration for the deposition of the Cycle-3 sediments. The regressive Cycle-3 produced the Meliat, Tabul, and Santul Formations which were deposited under a deltaic-transitional environment.
Due to the rapid deposition in deltas with an immense sediment supply, the heavy load that occurred re- juvenated old faults formed during Oligocene to Early Miocene. This re-juvenation took place contemporaneously with sedimentation, causing the appearance of growth faults. The growth of these faults were temporarily halted during the early
deposition of the Santul Formation because of a short transgressive phase. Faulting continued during Pliocene when the fourth cycle was deposited (Tarakan Formation).
The Late Plio-Pleistocene tectonic activity was compressive in nature, producing strike-slip faults. In several places the compression inverted the normal faults to become reverse faults. The last cycle (Cycle-5) saw the deposition of Bunyu Formation.
Based on the structural events and sedimentation processes, the Tarakan sub-basin can be divided into 5 distinct geological provinces: Daino-Sebuku Platform, S emb akung -B angkudulis GrabenISub Depocenter, Dasin-Fanny Ridge, Mintut-Tibi Slope, and Bunyu-Tarakan Main Depocenter (PERTAMINA, 1993) as shown in Figures 3 and 4.
Hydmcahon Generation
Of the 5 cycles deposited in the Tarakan sub-basin, only Cycles 3 and 4 have proven to be productive.
Hydrocarbons are commercially produced from the Sembakung-Bangkudulis Graben/Sub Depocenter and the Bunyu-Tarakan Main Depocenter. Within the other provinces only the Mintut-Tibi slope has shown non-commercial discoveries.
Within the Sembakung-Bangkudulis Graben/Sub Depocenter the productive reservoirs are the sandstones of the Meliat, Tabul, and Santul Formations. To the east in the Mintut-Tibi Slope and Bunyu-Tarakan Main Depocenter, the lithology of the Meliat and lower Tabul has changed to a more shale- dominant lithology. Good development of sandstones occurred only in the Santul and Tarakan Formations which have proven productive in Bunyu-Tapa and Tarakan Island fields.
Based on geochemical analysis, the source rocks are the shales of Meliat and Tabul Formations. In the Sembakung-Bangkudulis Graben/Sub Depocenter and Bunyu-Tarakan Main Depocenter, the sediments of these 2 formations are much thicker compared to the other provinces. This is because these two provinces occupied the space of the downthrown block of the growth faults that are trending southwest-northeast.
Taking a minimum cut-off of 300 m for shale thickness, vitrinite reflectance of 0.65 Ro, and a geothermal paleogradient > 3SoC/100 m y the kitchen
areas are concentrated in 2 areas: around the Sembakung-Bangkudulis Graben area and the Bunyu- Tarakan Main Depocenter south-eastward offshore separated by the Dasin-Fanny Ridge (Figure 5).
Laboratory analysis indicate that kerogen types are mainly gas prone type 111 kerogen with some oil-prone type I1 kerogen. Hydrocarbons were generated since the deposition of Santul Formation (Late Miocene).
Since the onset of generation, both associated (lateral) and disassociated (vertical) migration has taken place along the growth faults. Generally, migration from the eastern part of the kitchens follows a westward path along the regional dip.
Growth Faults
Growth faults are simultaneous with sedimentation.
And are generally formed because the sedimentation rate is high and includes coarse materials. Fault planes drop basinward, causing sediment accumulation on the downthrown side to be thicker than on the upthrown side. Growth faults have a hyperbolic shape in a vertical profile (listric). The fault dips at shallow depth may reach 45" to 60°, but with increasing depth there is a gradual decrease of dip and the fault plane becomes a bedding fault where the deepest strata consist of undercompacted shale (Busch and Link, 1985).
Bruce (1972) classified 3 types of growth faults commonly encountered based on the rates of deposition and subsidence (Figure 6). If the rate of deposition is faster than the rate of subsidence, which commonly occur during the regressive phase, the growth faults tend to prograde basinward forming a minor roll-over. These faults will form a listric-fault system whereby the older faults are located landward and the younger ones basinward. If the deposition rate is equal to the subsidence rate (stillstand), a main growth fault with a strong rollover feature and a large vertical displacement will result. If the deposition rate is lower than the subsidence rate, as is commonly found in the transgressive phase, then stepping faults will occur without roll-over. The first and second type of growth faults frequently occur in a regressive deltaic environment.
Method of Analysis
The evaluation of growth faults in the Tarakan sub-
basin is based on the tectonic and depositional history.
This paper tries to describe the characteristics of growth faults in each of the 5 provinces. The discussion includes the fault geometxy, the magnitude of the vertical displacement, the hydrocarbon content, the type of seals produced by the faults and a prediction of the hydrocarbon migration pathway. To measure the vertical displacement, the velocity values from the stacking velocity in seismic processing were used.
Faults analyzed are closely related with the drilled structures. Based on these analyses several conclusions are made regarding the sealing models and the mechanism of structural traps arising from the presence of the growth faults in the Tarakan sub- basin.
TARAKAN SUB-BASIN GROWTH FAULTS Growth faults developed in 4 of the 5 provinces in Tarakan sub-basin, the: Sembakung-Bangkudulis Graben/Sub Depocenter, Dasin-Fanny Ridge, Mintut- Tibi Slope, and Bunyu-Tarakan Main Depocenter. The Daino-Sebuku Platform province does not show indications oE growth faults, Structurally, this province is in a stable area (platform), thus only normal faults are present due to rifting that began in the Early Tertiary.
S embakung-B angkudulis Gmben
The Daino-Sebuku Platform and the Sembakung- Bangkudulis Graben provinces are separated by a normal fault trending southwest-northeast called the Sembakung-Bangkudulis fault. The fault extends more than 60 km and is a product of rifting that has taken place from the Oligocene to the Early Miocene. Since Middle Miocene this fault has undergone a re- juvenation and has developed into a growth fault at the same time as the Meliat, Tabul, and SantuI formations were being deposited during a regressive phase.
The growth faults in the Sembakung-Bangkudulis basins have different characteristics depending on their locations, even though they are still in one fault path. These differences are due to the different delta lobes being formed along the major fault.
Figure 8 shows a seismic line which crosses the
Sembakung-Bangkudulis fault and passes the Sembakung field. The major growth fault controlled the development of a strong roll-over structure. This in turn created a large anticline that produced a four- way dip seal. The vertical displacement ranges from 460 to 760 meters. Considering the large throw and the strong roll-over feature, it seems that this growth fault developed in a setting where the depositional rate was equal to the subsidence rate. There is also a contrast of thickness between the sediments in the downthrown side (thicker) and the upthrown side which seems to support this assumption.
Discoveries have been made in the Santul (oil and minor gas) and Tabul (gas) Formations. The hydrocarbons were generated from the Meliat Formation and the lower part of the Tabul Formation.
In this case, long-distance vertical migration has occurred, allowing the hydrocarbons to reach the Santul Formation. The active Sembakung-Bangkudulis fault is thought to have controlled vertical migration from the Meliat Formation to the Santul Formation (Figures 7, 8, and 9).
A Seismic line passing the Sesayap A-1 well shows a different picture (Figure 10). The growth faults of this area do not show a roll-over feature as strong as that in the Sembakung field. Because of this, the sealing feature is more of a roll-over against a fault and several synthetic faults grow out to the east of this major fault. Vertical displacement ranges between 250-380 meters. With depth these faults lose their angle and finally merge into one bedding plane.
This condition is controlled by faster deposition than subsidence. This is seen in the presence of thicker sandstone layers in the Meliat to Santul Formations.
Total thickness of sand penetrated in Sesayap A-1 well is 630 meters.
Hydrocarbons in the Sesayap A-1 well are found in the Meliat and Tabul Formations. Apparently vertical migration is not as extensive as in the Sembakung Geld. The presence of the thick sandstone layers probably impeded the vertical movement of hydrocarbons, thereby causing more lateral movement.
The shorter vertical displacement also restricts the migration along the major growth fault which is thought to be the main vertical thoroughfare for the hydrocarbons (Figure 1 I).
In the Bangkudulis area the growth faults show
another characteristic. Figures 12 and 13 are from a seismic line that crosses the Bangkudulis A-1 well and the section shows that the top of the Santul Formation has been eroded. Again, the vertical displacement is small (1 15-130 m), limiting the vertical migration of hydrocarbons and hence they are found only in the Meliat Formation. The unconformity between the Meliat and Tabul formations is also a problem in the migration of hydrocarbons.
Dasin-Fanny Ridge and Mintut-Tibi Slope
The Dasin-Fanny Ridge Province is separated from the Sembakung-Bangkudulis Graben province in the west by the Oligocene-Early Miocene fault. This fault parallels the Sembakung-Bangkudulis fault, but it has an opposite direction of throw. This province is characterized by shallow Economic Basement and thinner Cycle-3 sediments compared to those in the other provinces; even so, the growth fault is developed quite well in the area.
There is a significant difference between the growth faults in this province and these in the Sembakung- Bangkudulis Graben province. If the latter is rejuvenated from older faults formed during Oligo- Miocene time, the former is formed purely due to rapid sedimentation. It is also of a younger age, developing around the beginning of the deposition of the Tabul Formation (Late Miocene).
Figure 14 shows where the growth fault cuts the Tabul and Santul Formations? but at the top of the Meliat Formation they converged into a bedding plane, the whole appearance displaying distinctive listric faults.
Exploration drilling has not discovered hydrocarbons in the seals developed by the growth faults in this province. This may be due to its position which is far from the source rock, and the hydrocarbons were trapped closer to the source in the Main Depocenter province.
The growth faults in the Mintut-Tibi Slope province share characteristics with those in the Dasin-Fanny Ridge province, showing listric faults prograding eastward. The sediments are much thicker, controlled by[ a high regressive sedimentation rate (Figure 15).
Bunyu-Tar- Main Depocenter
The eastern-most geological province of the Tarakan sub-basin is the Bunyu-Tarakan Main Depocenter.
Sediments are much thicker and deeper compared to those in the other provinces. Besides Cycle-3 sediments, those from Cycled and Cycle-5 are also developed quite well and have not undergone any erosion caused by uplifts. Hydrocarbons are also generated within the younger formations: the top of the oil window is in the lower part of Tarakan Formation.
The growth faults that formed have an identical pattern to the faults in the Ridge and Slope provinces, but they are of a younger age (Mio-Pliocene). Figures 16 and 17 show the growth fault in the Bunyu and Tapa fields. The Tapa field is located on the downthrown side of the fault and contains gas trapped in closures that are controlled by the growth fault to the northwest. This fault does not have a strong roll- over feature, but it has a large vertical displacement of between 460 and 510 m. Gas reservoirs are found within the Tabul, Santul and Tarakan Formations.
Non-commercial hydrocarbons are also found in the Serban-1 well which is located on the downthrown side of the fault.
In the Bunyu-Nibung field, the closure is controlled by the growth fault in the form of a listric fault. The closure is to the southeast of the main fault, facing a synthetic fault. The Nibung and Bunyu structures are separated from each other by a fault, giving the impression that the Nibung structure is on the upthrown side of this particular fault. Hydrocarbons are proven in the Tabul, Santul, and Tarakan Formations. The oil is generally found at shallow depths, whereas the gas is trapped deeper (Figure 18).
The Tarakan field has 5 separate structures: Mengatal, Juata, Sesanip, Pamusian, and Mamburungan, and hydrocarbons are found within the Tarakan Formation.
All of these structures together form a closure in the form of a roll-over-against-fault feature. Figures 19 and 20 show the seismic cross section passing through the Sesanip structure. The distinguishing feature of this structure is that the fault controlling the closure is a reverse fault, the only one found in the Sesanip structure. The reversal in direction of a fault that was a product of the growth fault system may be due to the inversion processes caused by the latest tectonic activities (Figure 21).
THE ROLE OF GROWTH FAULTS
IN
HYDROCARBON ENTRAPMENT
The growth faults in the Tarakan sub-basin have double functions in the trapping mechanism of hydrocarbons. First, as a migration pathway, with the expectation that the faults are non-sealing. Second, in their further development, the faults can from traps by functioning as seals.
The assumption of growth faults acting as migration pathways depend on at least two conditions: migration occurs when the faults are still active, and hydrocarbons have already been generated. Within the Sembakung-Bangkudulis Graben province, growth faults started to develop in the Middle Miocene, contemporaneously with the deposition of the Meliat Formation. ,This continued right up to the deposition of the Santul Formation. At the same time, the shales of the Meliat and lower Tabul Formations started to generate and expel hydrocarbons. The still active faults became good pathways for vertical hydrocarbon migration. Lateral migration through layers also occurred, although it was probably not as prominent a mechanism because of the deltaic depositional setting of the formations that usually did not produce extensive lateral continuity.
Hydrocarbon migration through growth faults depends very much on how active the faults are, which in turn is controlled by the rate of deposition. The more active the fault is, the larger the displacement can be, allowing more hydrocarbon to migrate and also to travel farther. This condition is seen in the Sembakung field where hydrocarbons generated from the Meliat Formation are trapped in the Santul Formation (see Figure 9). The fault controlling the trap in the Sembakung field is active enough to form a strong roll-over feature. On the other hand, in the Bangkudulis structure the growth fault is not as active, thus hydrocarbon migration is restricted; in fact, they are found only in the Meliat Formation (see Figure 13). The Sesayap structure is interpreted to have features between those of the Sembakung and Bangkudulis structures (see Figure 11).
Within the Bunyu-Tarakan Slope province, hydrocarbons are discovered in the younger Santul and Tarakan formations. The migration mechanism is the same as that in the Sembakung-Bangkudulis Graben province, the difference is that it occurs at a
later time. Hydrocarbon generation, growth fault development, and migration started from Late Miocene to Pliocene (see Figure 18).
To function as hydrocarbon traps, ideally the fault plane of a growth fault should act as the seal. Some major conditions controlling this include lithological contact between the downthrown and the upthrown blocks, bedding position after faulting, and influence of pressure. Other conditions include the forming of gouges on the fault plane to create good seals.
However, understanding those conditions requires detailed study encompassing data from cores, logs (especially dipmeter log), and definite correlation from wells located facing the faults. Getting such data is still very difficult; nevertheless, this study will attempt to evaluate the influence of growth faults in the trapping of hydrocarbon, despite such constraints.
Fault planes can act as seals if the reservoir sand is juxtaposed to shale from the opposite block. Even though the reservoir does not form roll-overs, the shale can act as a seal and thus create an against-fault type of trapping.
The dip orientation of the layers on the upthrown and downthrown blocks also have an influence on the sealing properties of the fault plane (Allan, 1989). If the dip in the upthrown block is not the same as the dip in the downthrown block, the fault functions as a seal; however, if the orientations are the same, then the hydrocarbons have veIy good chances of escaping through the fault (Figure 22).
If pressures from the upthrown block are stronger than the pressures from the downthrown block, a sealing type of fault plane is formed. Weber et a1 (1978) noted that hydrocarbon trapping on the downthrown side of a growth fault in Nigeria is remarkably improved if reservoirs are juxtaposed against overpressured sediments (Figure 2 3 ) .
In the absence of a fault plane sealing, it is still possible to trap hydrocarbon, provided there is roll- over in the layer that comes into contact with the fault. Therefore the spill point is at the contact between the reservoir and the fault.
GROW^^ FAULT TFUPPING ~ O ~ ~ L
In the Tarakan sub-basin, hydrocarbons axe generally
trapped in the downthrown block of the main fault of a growth fault system. Several wells have discovered hydrocarbons on the upthrown block such as in the Serban-1 well, but due to small reserves they are not considered commercial. The tendency of hydrocarbons to accumulate in the downthrown block is anticipated as being controlled by the roll-over features that were created by the of growth fault.
During migration, the hydrocarbons followed the dip orientation of the sediments along the roll-over towards the closure on the downthrown block.
Considering the existing conditions discussed above and the drilling results so far, there are several hydrocarbon trapping models that can be proposed:
f o u r - w q dip closure, roll-over against fault, against fault, unconfomity truncated against fault (Figure 24).
Four-Way Dip Closurr
This closure is formed by a very active growth fault with a rapid subsidence rate which created a strong roll-over. The strongest intensity of the subsidence is at the lobe center of a deltaic deposition and close to the fault plane. Further away from the lobe and the fault, the intensity of the subsidence deminishes. A structure that is closed off from every direction is formed and can easily trap hydrocarbon; thus, the fault does not have to be sealing.
This model is observed in the Sembakung field.
Hydrocarbons migrated from the Meliat and Lower Tabu1 Formations through the main Sembakung- Bangkudulis fault. During vertical migration, when hydrocarbons reached the Santul Formation, the structure tilted eastward following dip orientation of the layers, going to higher position. This lateral migration went through a number of sandstone layers encountered in the Santul Formation of the Sembakung field. The hydrocarbon did not follow the fault plane further because the permeability of the sandstones was better than the permeability of the cracked zones of the fault.
Roll-over-Against-Fmlt
Basically the roll-over-against-fault model is the same as thi: €our-way dip closure model, except for the weaker roll-over feature on the growth fault. Contact between reservoir and fault plane is the spillpoint for hydrocarbons. The Hydrocarbon catchment area of
this model is smaller than the one for the previous model. This model is commonly seen in the Tarakan Island fields and the Tapa field.
Against Fault
One important criterion for this model is that the growth fault must be sealing, although before hydrocarbons were trapped the fault must have been non-sealing to allow migration. The change from non-sealing to sealing is controlled by lithological contact between sandstones and shales, opposite dip orientation of the layers in the downthrown and upthrown blocks. and pressure controls as discussed before. The against-fault model is not seen too often in the Tarakan sub-basin. Non-commercial discoveries include Mintut-1 and S. Sembakung-1.
Locally -U pthinw n- B 1 o clc-A g ai ns t-F aul t
This model is formed by prograding growth faults that created listric faults. Hydrocarbons mainly migrated through the main fault, although the synthetic faults can also function as pathways and trap the hydrocarbons in the upthrown block. Generally the position of this trap is in the downthrown block of the main fault. This model can be observed in the Sesayap structure and Bunyu-Nibung field.
This model is found in the Bangkudulis structure where there is an unconformity between the Meliat and Tabu1 Fomiations interpreted as a seal along with the fault plane.
CONCLUSION 1.
2.
3 .
There are 3 phases of fault development which shaped the hydrocarbon entrapment system in the Tarakan sub-basin: the Oligocene- Early Miocene Rift-faulting, the Middle Miocene growth-faulting, and the Late Miocene-Pliocene growth-faulting.
Growth faults in the Tarakan sub-basin have different characteristics depending on the rate of deposition and the rate of subsidence.
Hydrocarbon traps found in the Sembakung- Bangkudulis Graben and Bunyu-Tarakan Main Depocenter provinces are vely much dependent on the presence of the growth faults.
Vertical migration through faults at the time the growth faults are still active are more dominant than lateral migration through sediment layers.
Generally hydrocarbons are trapped in the downthrown block. If found in the upthrown blocks, the reserves are generally not commercial.
Hydrocarbon trapping models in Tarakan sub- basin are as follows: four-way dip closure, roll- over against fault, against fault, unconformity truncated against fault.
ACKNOWLEDGMENTS
The authors wish to thank the management of PERTAMINA Exploration and Production Directorate for allowing the publication of this paper; to Sebawang Shell, P.T. EXSPAN, and P.T. Genindo for their supporting data and helpful discussion; to Mr. Luki Samuel for his suggestions and advise.
REFERENCES
Allan, V.S., 1989, Model for Hydrocarbon Migration and Entrapment within Faulted Structures: AAPG Bulletin, v. 73, 803-8 11.
Bruce: C.H., 1972, Pressure Shale and Related Sediment Deformation, A Mechanism for Development of Regional Contemporaneous Faults:
Gulf Coast Association Geological Society, Transcript,
V . 22, 23-31.
Busch, D.A., and Link, D.A., 1985, Growth Faulting and its influence on Sedimentation and Prospect Analysis, In: Explorations Methods for Sandstones Reservoirs: OGCI Publications, Tulsa, 261 -284.
Downey, M.W., 1984, Evaluating Seals for Hydrocarbon Accumulations: AAPG Bulletin, v. 68, 1752-1 763.
PERTAMINA, 1993, Studi Regional Terpadu Blok S em b akung , C ekung an Tar ak an, Kalim ant an Tim ur Bagian Utara, internal publication.
Weber, K.S., Mandl, G., Pilaar, W.F., Lehner, F., and Precious, R.G., 1978, Growth Fault Structures: 10th Offshore Technology Conference, Paper 3356, 2643- 2653.
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POTENTIALLY POOR SEALING ATTITUDE
DIPS INDICATE POTENTIALLY GOOD SEALING ATTITUDE FIGURE 22
-
Dip Attitudes in Sediment (after Downey, 1984) \ TOP GEOPRESSURES -\ OBJECTIVE WEAK SEALING SURFACEI
GOOD SEALING SURFACE