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.

THE DEVELOPMENT OF KBS MODELING TO ASSIST MATRIX ACIDIZING TREATMENT (A PRELIMINARY STUDY OF THE ZELDA B-7 WELL)

PROCEEDINGS INDONESIAN PETROLEUM ASSOCIATION
Twenty-Eighth Annual Convention & Exhibition, October 2001

THE DEVELOPMENT OF KBS MODELING TO ASSIST MATRIX ACIDIZING TREATMENT
(A PRELIMINARY STUDY OF THE ZELDA B-7 WELL)

Ardian N.*

ABSTRACT

Current economic conditions have dictated that PSC operators maximize their production or accelerate the production of their reserves. One approach is to perform well stimulations. For decades, oil wells have been stimulated using various methods such as matrix acidizing and hydraulic fracturing. However, there have been advances in the stimulation processes both in knowledge and technology incorporated. One of the major PSC operators, Repsol-YPF Maxus SES, has claimed that the current success rate of their matrix acidizing practices is typically 30 to 40%. This is considered to be average. The success rate will rely on selection of the well candidates, acid types and additives. To improve the success rate, the use of a software package to perform the selection may not be sufficient anymore. The need to incorporate an integral approach using the database of experience, history and knowledge is recommended. The tool to accomplish this is called Knowledge Base System or KBS technology, considered “one of the applications of Artificial Intelligence in Expert Systems”.

* University of Indonesia

POLARIZATION HORN AS KEY IN IDENTIFYING RESISTIVITY CONTRAST AT HIGH ANGLE: AN OBSERVATION FROM SIX SUCCESSFUL HORIZONTAL WELLS, NATUNA SEA BLOCK B

PROCEEDINGS, INDONESIAN PETROLEUM ASSOCIATION
Twenty-Eighth Annual Convention & Exhibition, October 2001

POLARIZATION HORN AS KEY IN IDENTIFYING RESISTIVITY CONTRAST AT HIGH ANGLE: AN OBSERVATION FROM SIX SUCCESSFUL
HORIZONTAL WELLS, NATUNA SEA BLOCK B

Teguh Prasetyo*
Bambang S. Murti**
Sigit Suryonugroho***

ABSTRACT

Horizontal wells are judged to be the best alternative for depleting reserves efficiently and recovering optimum reserves from certain Conoco fields in Block B. From mid 2000 to early 2001, Conoco successfully drilled 3 horizontal gas wells and 3 horizontal oil wells. These wells achieved initial test flow rates ranging between 59 to 64 MMCFGPD in the gas wells and between 6,500 to 8,000 BOPD in the oil wells.

These successful results were achieved by careful pre- well design, incorporating 3D seismic and adjacent well data to better predict structural features and the petrophysical model of the planned well path. However, the subsurface remains uncertain. To help predict the landing point in the reservoir target, a polarization horn phenomenon is utilized. This phenomenon is an artifact of propagation resistivity tools, when approaching bed boundaries having great resistivity contrast, at high angle. Monitoring this effect while drilling is important because it can help determine whether a well should continue into its planned horizontal path, or needs to be side-tracked to an alternate location.

This polarization horn phenomenon and prediction of permeability using measured resistivity are the key tools used for geo-steering the successful horizontal wells.

* Conoco Indonesia Inc. Ltd.

** PT. Landmark Concurrent Solusi Ind. *** Baker Hughes Inteq

SLIMHOLE-TUBINGLESS: COST EFFECTIVE WELL ARCHITECTURE TO DEVELOP TUNU FIELD, MAHAKAM DELTA AREA - EAST KALIMANTAN

PROCEEDINGS, INDONESIAN PETROLEUM ASSOCIATION
Twenty-Eighth Annual Convention & Exhibition, October 2001

SLIMHOLE-TUBINGLESS: COST EFFECTIVE WELL ARCHITECTURE  TO DEVELOP TUNU FIELD, MAHAKAM DELTA AREA - EAST KALIMANTAN

Fata Yunus*
Benoit Ludot*

ABSTRACT

Until 1999, three well architectures were used for the “S” wells of the Tunu field: the “standard” design (last phase in 8”1/2 and 4”1/2 multi-packer completion in 7” liner), the “standard monobore” and the “slimhole monobore” (last phase in 6” and 4”1/2 monobore completion).

The generalization of light architectures was, however, impeded by several drilling and completion limitations in high-pressure regimes as well as the complexity of Tunu field where geological prognosis and reservoir pressure profiles are very difficult to predict.

In 2000 TotalFinaElf E&P Indonesie introduced the 4”1/2 tubingless completion in the delta, firstly to take the cost cutting process in Tunu drilling operations a “step further” but also with the ultimate objective to standardize the well architecture into a “all slimhole­tubingless” development.

Three tubingless completions were run successfully in the year 2000. An additional six tubingless completions were run in early 2001 with plans to complete more by yearend. The cost of tubingless completion wells to date ranges from 2,800 to 4,000 kUS$ for an average duration of 24 days (average 4,500 kUS$/35 days in 1999/2001). Recently, the rig was equipped with High Torque 4” DP to extend the slimhole -tubingless to long reach wells. The final cost saving for the first three years of the project is expected to reach 15 MUS$.

The slimhole -tubingless design generates significant cost and duration savings but additional risks need to be evaluated and controlled such as:

· no back up phase zones

· risk of differential sticking in slim hole in depleted zones straddled by two high pressure zones

· high drilling torque in 6” phase close to the limit of the equipment

· small rat hole and shoe track (down to 2/3 meters) as the well TD may be just a few meters after the last reservoir. The reduced safety margin for cement displacement can lead to low cement bond quality around the 4”1/2 shoe

· limited workover options

In January 2000, the first tubingless completion was run on TM-41 in the Tambora field to confirm the feasibility. Then two slimhole-tubingless completions were achieved in low pressure-low departure wells: TN-I3 in Tunu and TM-42.

Meanwhile a “all slimhole -tubingless” strategy was elaborated with the drilling, completion, geology, reservoir and well servicing departments, which was made possible thanks to a clear definition of the reservoir and production objectives.

In mid 2000 the drilling swamp barge was upgraded to 7500 PSI to extend the new design to 1.40/1.60 ESG reservoir targets.

In February 2001, the first six wells of the new drilling campaign have been drilled and completed slimhole -tubingless. The well cost ranges from 2,800 to 4,000 kUS$ for an average duration of 24 days.

The next step of the project took place in April 2001 when the rig was equipped with High Torque 4” DP to extend the slimhole-tubingless to long reach wells. The final cost saving for the first three years of the project is expected to reach 15 MUS$.

* TotalFinaElf E&P Indonesie