Introduction stratigraphy

Stratigraphy, a branch of geology, studies rock layers and layering (stratification). Stratigraphy, from Latin stratum + Greek graphia, is the description of all rock bodies forming the Earth's crust and their organization into distinctive, useful, mappable units based on their inherent properties or attributes in order to establish their distribution and relationship in space and their succession in time, and to interpret geologic history. Stratum (plural=strata) is layer of rock characterized by particular lithologic properties and attributes that distinguish it from adjacent layers.

History of stratigraphy begin by Avicenna (Ibn Sina) with studied rock layer and wrote The Book of Healing in 1027. He was the first to outline the law of superposition of strata:^[1] "It is also possible that the sea may have happened to flow little by little over the land consisting of both plain and mountain, and then have ebbed away from it. ... It is possible that each time the land was exposed by the ebbing of the sea a layer was left, since we see that some mountains appear to have been piled up layer by layer, and it is therefore likely that the clay from which they were formed was itself at one time arranged in layers. One layer was formed first, then at a different period, a further was formed and piled, upon the first, and so on. Over each layer there spread a substance of differenti material, which formed a partition between it and the next layer; but when petrification took place something occurred to the partition which caused it to break up and disintegrate from between the layers (possibly referring to unconformity). ... As to the beginning of the sea, its clay is either sedimentary or primeval, the latter not being sedimentary. It is probable that the sedimantary clay was formed by the disintegration of the strata of mountains. Such is the formation of mountains."

The theoretical basis for the subject was established by Nicholas Steno who re-introduced the law of superposition and introduced the principle of original horizontality and principle of lateral continuity in a 1669 work on the fossilization of organic remains in layers of sediment.

The first practical large scale application of stratigraphy was by William Smith in the 1790s and early 1800s. Smith, known as the Father of English Geology, created the first geologic map of England, and first recognized the significance of strata or rock layering, and the importance of fossil markers for correlating strata. Another influential application of stratigraphy in the early 1800s was a study by Georges Cuvier and Alexandre Brongniart of the geology of the region around Paris.

In the stratigraphy you can find term of

- Stratigraphic classification. The systematic organization of the Earth's rock bodies, as they are found in their original relationships, into units based on any of the properties or attributes that may be useful in stratigraphic work.

- Stratigraphic unit. A body of rock established as a distinct entity in the classification of the Earth's rocks, based on any of the properties or attributes or combinations thereof that rocks possess. Stratigraphic units based on one property will not necessarily coincide with those based on another.

- Stratigraphic terminology. The total of unit-terms used in stratigraphic classification.It may be either formal or informal.

- Stratigraphic nomenclature. The system of proper names given to specific stratigraphic units.

- Zone.Minor body of rock in many different categories of stratigraphic classification. The type of zone indicated is made clear by a prefix, e.g., lithozone, biozone, chronozone.

- Horizon. An interface indicative of a particular position in a stratigraphic sequence. The type of horizon is indicated by a prefix, e.g., lithohorizon, biohorizon, chronohorizon.

- Correlation. A demonstration of correspondence in character and/or stratigraphic position. The type of correlation is indicated by a prefix, e.g., lithocorrelation, biocorrelation, chronocorrelation.

- Geochronology. The science of dating and determining the time sequence of the events in the history of the Earth.

- Geochronologic unit. A subdivision of geologic time.

- Geochronometry. A branch of geochronology that deals with the quantitative (numerical)measurement of geologic time. The abbreviations ka for thousand (103), Ma for million (106), and Ga for billion (milliard of thousand million, 109) years are used.

- Facies. The term "facies" originally meant the lateral change in lithologic aspect of a stratigraphic unit. Its meaning has been broadened to express a wide range of geologic concepts: environment of deposition, lithologic composition, geographic, climatic or tectonic association, etc.

- Caution against preempting general terms for special meanings. The preempting of general terms for special restricted meanings has been a source of much confusion.

PROCEEDINGS JOINT CONVENTION BALI 2007
The 32^nd HAGI, The 36^th IAGI, and The 29^th IATMI Annual Conference and Exhibition

FOLD GENERATE FAULT STUDY IN SEMAYANG AREA,
EAST KALIMANTAN

Fuad Ahmadin Nasution (¹), Armein Suleiman (^1,2), Andang Bachtiar (³)

(1) GDA Consultant
(2) Magister Program, Department of Geology, Institute of Technology Bandung
(3) Exploration Think Tank Indonesia (ETTI)

ABSTRACT

This study is referring to Mitra’s theory and models, 2003 which is study of fold development which generate secondary fault known as fold accommodation fault. Fold accommodation fault are secondary faults that accommodate strain variations related to structural and stratigraphic position during fold evolution. Four main fault accommodation faults are commonly fault found. Out of syncline and into anticline thrusts form primarily because an increase in bed curvature within fault. Forelimb and backlimb thrusts form by a variety mechanisms. Forelimb space accommodation thrusts are low displacement thrust that resolves strain discontinuities resulting from increased curvature in fold cores. Forelimb shear thrusts form in late stage of folding because of rotation and layer-parallel extension on the steep forelimb of folds. Most of backlimb thrust is originated as out of syncline thrusts.

This study intended to analyze the fold generate fault based on application of fold accommodation fault theory and its type which is found in study area. The study is focused on syncline and anticline in the Semayang area where is situated in Kutai basin, East Kalimantan. An understanding of kinematic evolution and slip distribution of fault in Semayang area is important to developing accurate interpretations of structures beside the models of structures constructing balanced cross sections and interpreting of geometry hydrocarbon trap forming structures. On the other hand, slip distribution of these kinds of fault is important to describe fault sealing capacity of related fault.

The structural formed due to tectonic event in Kalimantan since Middle Miocene (15-1 0Ma) which formed northeast-southwest trending Mahakam foldbelt. It is believed there some deltas were developed during that times formed huge sedimentary accumulation in the basin which were gave encumbering of sedimentation that triggering basin subsidence and structural forming. Skin-thin tectonic deformation also contribute to forming structures with developing of decollement zone on massive pro-delta deposits which were forced by tectonic sliding of the highs on the edge of Kutai basin to start resulting the anticlinorium.

About seven seismic lines interpret to define the fold accommodation fault pattern. The interpretation results was found five of some common types of faults accommodation faults are; out of syncline thrust propagating on the gently dipping limb, limb wedge thrusts (Figure-1), hinge wedge thrusts, forelimb and backlimb thrusts.

In conjuction to tectonic, some publication has been informed reconstruction of tectonic evolution in Kutai Basin. Early publication interpret that the tectonic is forming due to reactivated graben at second due to collision on North West Borneo Margin and East Sulawesi subduction in Mid Miocene (McClay, 2000) and Late of Early Miocne (Chamber et al, 1995). On the other hand, another hypothesis interprets that uplift and tectonic event is not relates to Sulawesi Collision (Calvert and Hall, 2003). Refer to these hypotheses, source of fold accommodation fault requires more discussion to summarize which one of the tectonic impact influence to form fold accommodation fault. Current analysis has been generated some

PROCEEDINGS JOINT CONVENTION BALI 2007
The 32^nd HAGI, The 36^th IAGI, and The 29^th IATMI Annual Conference and Exhibition

hypothesis that secondary fault is forming due to collisions of North West Borneo margin which is interact with prodelta shales. This hypothesis is generated based on occurrence of mud volcano adjacent study area and the presence of regional overpressure which refer of some publication (Bates, 1996).

The implication of this study is to review hydrocarbon potential in Semayang Area. The occurence some oil field and also oil and gas seepage adjacent area is informed that petroleum system occur inside study area. Three petroleum system has been defined in Kutai Basin are; Upper Neogene whereas source rock was generated from Midlle to Miocene Balikpapan Group and Late Miocene to Pliocene Kampung Baru Formation, the migration process is continuous and beleived to be started in Late Miocene to Pliocene time, and still most probably being occured at present day, Lower Neogene Petroleum System whereas source rock was generated from Miocene coals and carbonaceous shales of deltaic associated sediments. Time of migration was probably conducted during Middle Miocene to Late Miocene. Paleogene times whereas source rock is marine shale of Middle to Late Atan Formation. Time of migration was unknown (Pertamina BPPKA, 1997, Paterson et al, 1997). Clastic sediment and Reefal Carbonate are well known as potential reservoir in Kutai Basin. Turbidite reservoir in Pulau Balang Formation and Deltaic Sediment in Kampung Baru and Balikpapan Formation has been established contained hydrocarbon. Intraformational seal is interpreted to be potential seal in Semayang Area. The result of study interpret that hinge wedge thrust is potential trap; (Figure-2) the results of analysis which is incorporating with theory indicate that the geometry or reservoir is thick due to increased thickness on compression stage beside the sealing fault could be occurred during fold evolution.

Minifract

PROCEEDINGS JOINT CONVENTION BALI 2007
The 32^nd HAGI, The 36^th IAGI, and The 29^th IATMI Annual Conference and Exhibition

Modifikasi Minifract Pada Kondisi Tortuosity di Sumur Dengan
Permasalahan Kerusakan Perforasi.

Hisar Limbong dan Sumadi Paryoto

Teknik Produksi-Reservoir / Engineering
PT.Pertamina EP Region Jawa

ABSTRACT

Minifract have been recognized and well used as the most accurate method to determine data in Fracturing design. Minifract is a pumping treatment with a non compressible fluid which is designed to be as closed as possible to the actual treatment (Mainfract), without using any proppant/sands.

However in the well with tortuosity problem, the application of minifract pumping will meet constraint because of increasingly surface pressure higher compared to the low pumping rate. Tortuosity is the creation of small fractures leading from perforations that may or may not fully connect to the main fracture during hydraulic fracture operations. Tortuosity can caused premature screen out, which is sand/proppant can’t be delivered successfully through well bore. And make the result of gain production less than expectation; in worst case it will make the well lost. Tortuosity phenomenon can be identified with step rate test method. At step rate down phase, which is part of step rate test, this phenomenon can be indicated by doing curve analyze by plotting data between pressure and pumping rate.

The purpose of this paper is to present a situation/case which is the phenomenon of tortuosity is not clearly identified, thus the application of minifract pumping wouldn’t reach as ideal pumping rate as is wanted because tortuosity create pressure drop between well bore and fracture zone. This distinctive case of unidentified tortuosity phenomenon caused by perforation damage of the well bore. The modification of minifract is done by pumping slug method to overcome tortuosity effect, so that pumping rate can achieve as high as its wish without any constraint of surface pressure.

Keywords : Minifract, Tortuosity, Step Rate Down, Pumping.

PROCEEDINGS JOINT CONVENTION BALI 2007
The 32^nd HAGI, The 36^th IAGI, and The 29^th IATMI Annual Conference and Exhibition

TSUNAMI INUNDATION MODELING
PELABUHANRATU, WEST JAVA

Yudhicara
Center for Volcanology and Geological Hazard Mitigation
ABSTRACT

According to its coastal characteristic, Pelabuhanratu and its surroundings is divided into 4 (four) types, they are : (1) sandy beaches, (2) gravely sandy beaches, (3) rocky beaches and (4) corral reef beaches. In general coastal area of Pelabuhanratu has bay shape and pocket beaches. Has low-steep morphology, flat area has 6.5 km at Ciletuh Bay and maximum ~ 9 km at Pelabuhanratu bay. Beach slope 2o to 10^o. Height difference of low land from sea level is about 1 to 6 meter. Horizontal distance to the nearest building 40 - 175 meter.

Using ComMIT (2007), we tried to model tsunami inundation. We used two scenarios. Scenario 1 has source model perpendicular to Pelabuhanratu. We were using three sub-faults from Sunda subduction zone which has earthquake rupture length 300 km and 50 km width, magnitude as Mw 9.0, distributed slip 59.14 meters, which has fix depth (~10 km), dip (~25^o) and rake angle (90^o). The result has maximum flow depth about 10 meters near to the shore and maximum inundation about 6.48 km from the shoreline.

Scenario 2, has source model not perpendicular to the site but earthquake parameter is the same. The result has maximum flow depth about 6 meters and maximum inundation about 3.24 km.

Keywords: Tsunami inundation model, earthquake sources, coastal characteristics

THE EFFECT OF DUCTILE COMPONENTS AND CLAYS OF SHALY SANDSTONE ON RESERVOIR QUALITY REDUCTION

PROCEEDINGS JOINT CONVENTION BALI 2007
The 32^nd HAGI, The 36^th IAGI, and The 29^th IATMI Annual Conference and Exhibition

THE EFFECT OF DUCTILE COMPONENTS AND CLAYS OF SHALY SANDSTONE ON RESERVOIR QUALITY REDUCTION

Junita Trivianty Musu¹ and Bambang Widarsono^1
1 R and D for Oil and Gas Technology “LEMIGAS”
ABSTRACT

Ductile components including rock fragments, clay, and matrix material are often considered as the most important factors that control quality of shaly sandstones, which are usually characterized by low porosity and permeability. In presence of ductile components, the degree of quality reduction is affected mainly by distribution, occurences, and amounts of the ductile components. Therefore, presence of ductile components affect rock petrophysics, and consequently has effect on fluid movements in reservoir during production.

This paper presents results of the study on plug samples taken from five wells from various fields in Cooper Basin (Tirrawarra Sand), South Australia. The samples were studied petrographically using x-ray diffraction, optical petrography, and scanning electrone microscope. The results were integrated with routine and special core analysis data. The overall results shows that the distribution and the amount of ductile components have significantly reduced porosity, hence the quality of the reservoir. However, the effect is different for different types of porosity, and this certainly add valuable addition to our understanding over permeability behavior of shaly sandstones.

CHARACTERIZATION AND EXPERIMENTATION OF INDIRECT CARBONIZATION TO KOTABANGUN COAL, TENGGARONG, EAST KALIMANTAN

PROCEEDINGS JOINT CONVENTION BALI 2007
The 32^nd HAGI, The 36^th IAGI, and The 29^th IATMI Annual Conference and Exhibition

CHARACTERIZATION AND EXPERIMENTATION OF INDIRECT CARBONIZATION TO KOTABANGUN COAL, TENGGARONG, EAST KALIMANTAN

M. Ulum A.Gani

Research Center For Geotechnology, Indonesian Institute of sciences -LIPI
Jl. Cisitu-Sangkuriang, Bandung 40135
Tlp: 2507771, Fax: 2504593
E-Mail: ulumgany@yahoo.com

ABSTRACT

Characterization and experimentation had been carried out to Kotabangun coal, Tenggarong, East Kalimantan.

Characterization is performed by some analysis comprising of Proximate analysis (moisture content, volatile matter, ash content, and fixed carbon), Ultimate analysis (the constituent of C, H, O, N. S) and petrographycal analysis (vitrinite, liptinite and inertinite, vitrinite reflectance), while the experimentation is conducted by using carbonization drum with indirect carbonization used carbonization temperature ranging 400-700^oC for approximately 20 hours.

The result of carbonization (semi coke) indicates that the decreasing of weight of 34.43 % for particle size of 1 cm, 39.58 for particle size of 2 cm, and 36.40 for particle size of 3 cm, while moisture content, volatile matter and sulfur content decreasing weight of 19.53 %, 49.20 % and 17,64 % respectively, while ash content, fixed carbon and caloric value increase of 40.04 %, 27.09 and 20.91 % respectively.

Key words : characterization, experimentation, indirect carbonization, semi coke