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.

CHALLENGES AND SOLUTIONS IN PLANNING AND OPTIMIZING A HORIZONTAL WELL IN SOUTH SUMATRA, INDONESIA

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

CHALLENGES AND SOLUTIONS IN PLANNING AND OPTIMIZING  A HORIZONTAL WELL IN SOUTH SUMATRA, INDONESIA

John Wasson*
John Pairaudeau*
Rahmad Wibowo*
Suwardji*
Hidayat Abqory*
Mike Pearson**

ABSTRACT

JOB Pertamina-Seaunion Energy (Limau) Ltd. drilled its first horizontal well in the Q-51 Block of the Limau Oil Field, South Sumatra, Indonesia in September, 1999. The primary objective was to improve production performance and oil recovery from a mature oil field that faces escalating water cuts and production decline. The reservoirs are massive stacked channel / alluvial sandstones, with excellent porosity and permeability, occurring in thick, stacked- sand sequences. Water coning in vertical wells has been partially controlled in recent years with reverse coning installations (dual oil-leg/water-leg completions).

Reservoir numerical simulation modeling was used to history match existing vertical wells and to forecast production from possible horizontal well locations across the top of the remaining oil pay. A detailed drilling plan was prepared for drilling a horizontal sidetrack through a “window” cut in the casing of an existing vertical well. The well was successfully drilled and a 215-meter horizontal section of excellent oil pay was completed open-hole, with an uncemented pre-perforated liner.

The well produced clean oil during the first five weeks of production; however, after that, the water- cut steadily increased. A bottomhole flowing and shut-in pressure survey was conducted and the test analysis indicated that the pressure drawdown was very low, that only 5-10% of the total pay section was effectively producing, and that the wellbore skin was negative. Later, a mud clean-out job and production logging survey was performed, which showed no improvement and that all of the production was coming from a short section at the toe of the well. It was concluded that the wellbore has encountered a very high permeability layer that is causing the water problem and that it may be possible to close this off. It was also concluded that a completion method allowing more isolation control of the wellbore should be utilized on future horizontal wells of this nature.

 

* JOB Pertamina-Seaunion Energy (Limau) Ltd. ** Schlumberger Oilfield Services

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

DRILLING WITH CASING – PRACTICAL, COST EFFECTIVE AND HERE TO STAY

Mike Wardley*
Ary Priadi**
Ken Dalrymple***

ABSTRACT

For several years, Drilling with Casing has been something of a ‘Cinderella’ technology, trapped between a few successful niche applications and a perceived need to fully emulate the capability of conventional drilling.

Over the five years up until the end of 1999, various niche applications were successfully addressed, but the technology had not been applied economically to mainstream drilling operations.

Since early 2000, developments have taken place rendering drilling-down surface casing a standard operation in several parts of the world, most notably in Thailand and Indonesia. The enabling technology has been a drillable drill bit (or ‘DrillShoe’). Unlike conventional oilfield bits, which are inherently non- drillable, this tool is constructed from soft alloy and contains a cutting structure, which does not damage the next bit in the hole.

The DrillShoe method is the first truly ‘single-trip’ technique of drilling with casing – nothing is pulled out of the hole. Casing is drilled down in precisely the same manner as conventional rotary drilling with drill pipe. When TD is reached, cementing can begin immediately. The next drill string is run in conventional manner and drills-out the shoe track and DrillShoe, without damage to the drill bit, which then proceeds to drill the next section of well bore.

In the year to Jun 2001, more than 100 Drilling with Casing operations have been completed successfully with this technology. Casing sizes vary from 7 in. to 20 in., with run lengths up to 1500 feet. Case histories are presented showing the development of tools and drilling practices.

 

* BBL Downhole Tools ** Pertamina-YPF Maxus *** BBL Asia Pacific

POTENTIAL APPLICATION OF GAS TO LIQUID (GTL) TECHNOLOGY ON NATUNA’S HIGH CO2 CONTENT NATURAL GAS FIELD

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

POTENTIAL APPLICATION OF GAS TO LIQUID (GTL) TECHNOLOGY ON NATUNA’S  HIGH CO2 CONTENT NATURAL GAS FIELD

A. Hanif*
T. Suhartanto*
A.P.E. York**
M.L.H. Green***

ABSTRACT

One of the major natural gas reserves in Indonesia is found in the Natuna ‘D Alpha’ gas field. This is not only a large gas deposit (222 TCF), but is also interesting because it is composed predominantly of CO2 (71%). The last development scheme proposed by the oil companies Exxon and Pertamina for the utilisation of this gas, before the crisis of 1997, was for the CH4 to be sold as LNG, while the CO2 was to be injected back below the ocean floor. However, the marketing of natural gas depends on long-term and high-risk contracts or requires strong commitment between the producer and the buyer, even long before the development stage.

An alternative marketing strategy would be to convert the natural gas mixture to syngas (CO + H2) by the partial oxidation and dry reforming of methane with carbon dioxide; the syngas can then be used for the production of a wide variety of chemicals and fuels using gas-to-liquids (GTL) technology, e.g. Sasol or Shell’s SMDS.

This has three major advantages compared with the LNG route: i) less separation stages will be needed and the cost of gas injection below the sea floor will be lower, since there will be much less CO2 remaining after the reforming process; ii) dry reforming is an effective way of incorporating CO2 in the products, which will eventually end up, for example, as fuel powering an engine; and iii) the prices of the end products are much higher and easy to market as compared with LNG. In this study, it will be shown that molybdenum and tungsten carbide catalysts are active and stable for the process of partial oxidation and methane dry reforming to syngas using a feedstock of high CO2 content natural gas, such as that found in the Natuna ‘D Alpha’ field, Indonesia.

* Pertamina

** Johnson-Matthey, Sonning Common, Reading, U.K. *** University of Oxford, U.K.

APPLICATION OF RESERVOIR MANAGEMENT TECHNIQUES TO IMPROVE RECOVERY FROM A MATURE WATERFLOOD PROJECT IN SUMATRA

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

APPLICATION OF RESERVOIR MANAGEMENT TECHNIQUES TO IMPROVE RECOVERY FROM A MATURE WATERFLOOD PROJECT IN SUMATRA

Sami Bou-Mikael*
Gerald H. Schmit*
Aminin Fanandi*

ABSTRACT

Discovered in 1944 and placed on production in 1952, Minas is a world class field that has produced 4.27 billion barrels of oil to date, a recovery of ~5 1% of OOIP. Current production average is 130 MBOPD and 5600 MBWPD (97.7% water cut). Primary production was supported by a weak aquifer until the early seventies when Caltex Pacific Indonesia (CPI) initiated the peripheral water flood (PF) for pressure maintenance purposes. Following the peripheral flood CPI initiated pattern water flood (PWF) in 1993 using a 71 acre inverted 7-spot pattern program. The initial results of the pattern water flood were encouraging.

Recently Minas started to experience a steeper production decline and higher operating costs raising questions about the waterflood operation. Minas strategic business unit (SBU) initiated a waterflood optimization study to identify, field-test and develop a comprehensive reservoir management strategy that will improve recovery, stabilize production and reduce the field operating cost. The main challenges facing Minas today are: increasing water production, high water cut, escalating power requirement and cost, water disposal, capacity of existing facilities, increasing reservoir pressure, inadequate vertical and horizontal sweep efficiencies and steep production decline.

This paper outline the asset management strategy developed to address the above challenges with creative solutions:

· Shift from commingled to single zone completion to improve vertical sweep efficiency, reduce water recycling and eliminate cross-flow. Water production was reduced by 40% from a single gathering station.

· Water shut-off efforts over the past 10 months resulted in $10 million saving in annual operating costs.

· Build a fine-scale geostatistical model to support a flow simulation model used to test various alternatives to improve areal sweep efficiency through pattern realignment.

· Improve completion efficiency through
application of saturation logs, under-balanced perforations, washing perforations and dual down hole pumping system.

Reduce the reservoir pressure from 550 to 325 psi to improve flood efficiency

* P.T. Caltex Pacific Indonesia