Mahakam Delta Research Articles

Late-Holocene evolution of the Mahakam delta, East Kalimantan, Indonesia

The late-Holocene Mahakam delta, located along the tropical eastern shore of Kalimantan, Indonesia, is considered to be a textbook example of a mixed tide–fluvial dominated delta system. The delta prograded about 60 km during the past 5000 years, which led to the development of a distinct network of distributary and tidal channels. Wave action is low due the limited fetch in the narrow strait of Makassar. Mahakam River discharge is about a quarter of the Mississippi River discharge and is characterized by absence of flood surges. Therefore, natural levees, crevasse splays and avulsions are absent in the delta plain. For the past four decennia, both modern and ancient Mahakam delta deposits have been studied in detail in order to better understand subsurface Miocene and Tertiary Mahakam deposits, which host large volumes of hydrocarbons. This study focuses on the dynamics and stratal patterns of delta plain, delta-front platform deposits and suspended sediments. Due to the predominance of semi-diurnal tides and the associated flow reversals, depositional patterns are highly variable which has resulted in the formation of characteristic sand–mud couplets. The distribution of the sand–mud couplets found in this study differs from previously proposed conceptual models. They are limited to the fluvial domain and form in the distributary channels (lateral channel bar) or at the fluvial dominated delta-front platform, which flanks the mouth bar deposits in offshore direction. The sand–mud couplets which formed as delta-front platform and lateral channel bar deposits are similar and can only be identified based on their 14C age. The sand content decreases significantly towards the tidal dominated areas due to limitation in transport capacity. Turbidity measurements taken in front of the river mouth also show rapid settlement of river plume sediments. Some 22 new AMS 14C dates show that late Holocene sea level history resembles the eustatic sea level curve giving a first approximation of the Late Holocene sea level history for East Kalimantan. The dates suggest that the progradational delta system evolved under conditions of slowly rising sea level, which compares well to the eustatic sea level curve. In addition, calculated averaged deposition rates of the sand–mud couplets indicate that deposition is driven by the spring–neap tide cycles instead of the daily tidal cycle.

The influence of basement faults during extension and oblique inversion of the Makassar Straits rift system: Insights from analog models

Analog models were used to investigate the influence of cross-trending basement faults on inverted rift systems similar to those located in the Makassar Straits. Multilayer models composed of sand, silicone putties, and a silicone-plasticine mixture were constructed so that laterally offset rift basins would form on either side of a preexisting basement fault. Transfer zones comprising a series of en echelon normal faults that connect downward with the basement fault formed to link the laterally offset rift basins during the extension phase. Subsequent oblique inversion of the models resulted in a general progression starting with broad folding, followed by the development of small-scale inversion anticlines associated with reactivated rift faults, to thrust faulting, and finally, to the formation of cross-trending wrench faults. Rift fault reactivation and wrench fault development were prominent in the transfer zones because of the orientation of the constituent faults (oblique to the shortening direction) and their connection with the underlying basement fault. The addition of an intrasedimentary detachment layer, which represents a thick overpressured shale present in the vicinity of the economically important Mahakam delta, allowed gravitational collapse and extensional faulting to occur on structural highs. The cross-trending basement fault was again the locus for inversion structures, both above and below the detachment layer in the latter case, which may have influenced the distribution of petroleum in the region.

Development of Equatorial Delta-Front Patch Reefs During the Neogene, Borneo

Abstract Miocene patch reefs formed in turbid waters associated with high siliciclastic input at the seaward margin of the equatorial Mahakam Delta in eastern Borneo, SE Asia. Patch reefs were initiated on unstable substrates on localized low-relief bathymetric highs associated with delta-front channels or distributary mouthbars in the process of abandonment. Patch reefs developed only in shallow waters, formed low-relief buildups, lacked rigid frameworks, and had gently sloping margins. Although the biodiversity of the patch reefs may be comparable with that of clear-water systems, all the organisms present were adapted to turbid-water areas associated with siliciclastic, and sometimes nutrient, influx. The patch reefs were transient features, and their demise was influenced by increased siliciclastic and nutrient input, perhaps at times associated with deepening. Carbonate production and bioherm or patch-reef development can occur in turbid-water delta-front areas as localized or more regionally extensive units during any phases of eustatic sea level. However, development and preservation of turbid-water carbonates is most likely during relative transgression or perhaps late lowstand periods. This is in contrast with common highstand carbonates from clear-water shelves, where nearly pure carbonates interdigitate with siliciclastics. It is the interplay between factors such as tectonics, eustasy, delta lobe switching, shelf currents, and amount and size fraction of siliciclastic influx that ultimately controlled carbonate development and preservation.

マハカムデルタ地域の石油探鉱における石油システム概念の歴史と機能

マハカムデルタ地域の石油探鉱における石油システム概念の歴史と機能

Lookback on Performance of 50 Horizontal Wells Targeting Thin Oil Columns, Mahakam Delta, East Kalimantan Part B: Lessons Learned From Performance Lookback

Abstract The objective of the study is to provide lessons learned from the actual well performance data, which is provided in Part A of this paper(1), which will improve future well planning as horizontal wells continue to be used in the fields offshore East Kalimantan, Indonesia. Practical issues related to well planning, such as selection of well location, well length, well path, and standoffs to fluid contacts, are presented. The paper also discusses specific operational strategies used in drilling, completing, and producing these horizontal wells. Results from the well performance data provide guidelines and refinements for continued implementation of horizontal wells to optimize thin oil column development in these fields. Introduction The development of thin oil columns has been a challenge that operators have faced over the years(2–5). In the 1990s, more and more horizontal wells were drilled to tackle this class of reservoir problem. Part A of this paper(1) presented a lookback of over 50 horizontal wells, targeting thin oil columns that Unocal Indonesia FIGURE 1: A preferable simple horizontal well path. Available in Full Paper. Company has drilled since 1996 in their offshore fields in East Kalimantan, Indonesia. This paper presents a discussion related to the data from actual well performance as related to reservoir aspects of those horizontal wells. Common lessons learned and practical considerations used in planning and operating these horizontal wells are summarized. Then, a discussion on continued refinements for these practices for future use is provided. Lessons Learned The authors present a summary of common observations and lessons learned from drilling and exploiting the thin oil reservoirs discussed in Part A of this paper(1). Best practices based on performance lookback are drawn and presented. Pre-Well Planning Organization plays an important role in the operations of these reservoirs when dealing with horizontal drilling. Cross-functional teams have been focused on exploitation of these reservoirs to FIGURE 2: An undulated well path to search for WOC before completion. Available in Full Paper. FIGURE 3: Oil recovery increasing with decreasing cumulative GOR. Available in Full Paper. optimize asset values since horizontal pre-well work typically requires much more effort compared to that of a conventional well. Specialty support groups, such as reservoir modelling and analysis and cross-disciplined chiefs, play a key role in assisting asset teams in well planning, projects QA/QCs, and lookback. The batch drilling of wells to maximize rig time efficiency requires a careful well-by-well plan and a contingency plan ahead of time since urgent decisions concerning setting landing points, selecting well courses, and completion techniques often arise due to unexpected events or surprises while drilling. Geological risk remains a key factor in well planning, even when the target reservoirs are thought to have sufficient well control. The key challenge is to assess the current fluid contacts and thus the oil column thickness in the target area. Running saturation logs (e.g., RST) and reservoir modelling could help assess and confirm current fluid contacts. Awareness of uncertainty in logging tool depth (+/-1.5 m) helps to plan for selecting prudent landing points.

Lookback on Performance of 50 Horizontal Wells Targeting Thin Oil Columns, Mahakam Delta, East Kalimantan Part A: Well Performance Data

Abstract Paper A presents a case study to look back on the performance of over 50 horizontal wells drilled in three different fields in the Mahakam Delta, offshore East Kalimantan, Indonesia. The common application of these horizontal wells is to produce thin oil bands sandwiched between a gas cap and a bottom/edge aquifer. Based on well performance data, the lookback is mainly focused on the reservoir evaluation aspect of these horizontal wells. Reservoir and well performance is analyzed using a variety of techniques, varying from single-well analytical modelling (or decline curves) to more complex reservoir simulation. Based on statistical data resulting from the analysis of these wells, specific relations between reserves and reservoir-well parameters are identified which will be useful for predicting future well performance, especially during early prognosis. Introduction The development of thin oil columns has been a challenge that operators have faced over the years(1–4). The key concern is economic and optimal operations, as coning could cut short production and hinder recovery. Many authors have looked at this problem and suggested ways to lengthen well or reservoir life by reducing coning. In the 1990s, more and more horizontal wells were drilled to tackle this class of reservoir problem. Although observations about their success have been mixed, horizontal FIGURE 1: Rate control to maximize oil recovery from thin oil column. Available in Full Paper. wells generally have been accepted as a way to improve recovery compared to conventional wells. On individual projects, factors that need to be compared include considerations for stacked pay completion, drilling and completion techniques, future well workover plan, slot availability, and project cost. This paper presents a lookback of over 50 horizontal wells, targeting thin oil columns with gas cap and water leg, that Unocal Indonesia Company (UIC) has drilled since 1996 in their offshore fields in East Kalimantan, Indonesia. As these wells are intended to minimize coning effects for improving recovery, the objective is to observe actual well performance as related to reservoir well properties to provide a basis for improving future well planning and operations. Practical issues related to well planning, drilling and completion methodology, and operations are also discussed. First, a general discussion of fluid flow behaviour and parameters affecting thin oil column exploitation is presented. A brief description on the evaluation techniques used in the performance lookback follows. A discussion specific to data from the three particular fields operated by UIC in East Kalimantan is then presented. Fluid Flow Behaviour in a Thin Oil Column Oil and gas recovery from a thin oil column under the influence of gas cap and water support is strongly dependent on oil column thickness, formation permeability, gas cap size, aquifer strength, FIGURE 2: Effects of completion standoff to GOC and gas cap size on recovery (1 Bcf / MMBo = 178.1 m3/m3). Available In Full Paper. TABLE 1: Summary of field data. Available In Full Paper. FIGURE 3: Contribution of horizontal wells to the total Attaka oil production. Available In Full Paper.

Modeled shale and sandstone burial diagenesis based on the K-Ar systematics of illite-type fundamental particles

AbstractThe clay fraction of the sedimentary succession beneath the Mahakam Delta (eastern Kalimantan, Indonesia) consists mainly of mixed-layer illite-smectite, with minor amounts of kaolinite and/or dickite, discrete detrital illite and chlorite. On the near-shore anticline, evolution of this mixed-layer material is characterized by a decrease in expandability with depth. The mechanism of conversion of smectite to illite layers depends on the lithology of the host rocks: it evolves along a solid-state transformation in the shales and a dissolution-precipitation in the sandstones.Illite fundamental particles from two sandstones buried at ∼4000 m in the Tambora field next to the Handil field on the same near-shore anticline yield a mean K-Ar age of 15.7±1.6 Ma (2σ), which is younger than the stratigraphic age but still slightly biased by minute amounts of discrete detrital illite. Recalculated after modeling, which takes into account the occurrence of the discrete detrital illite, this K-Ar age becomes 14.4±0.7 Ma. The K-Ar values of the fundamental particles from associated buried shales are significantly older, which can be explained by a mixture of (1) a precursor material similar to that presently deposited in the delta of the Mahakam River, and (2) authigenic fundamental particles incorporating Ar with a 40Ar/36Ar ratio above atmospheric value during nucleation and growth on the same detrital precursor.Application of the modeling to the burial evolution of <0.4 µm particles from both the shales and the sandstones of the basin points to a contribution of detrital micaceous material in both lithologies, (1) in the sandstones as a detrital component dissolving progressively and mixed mechanically with the authigenic fundamental particles, and (2) in the shales as a detrital precursor progressively releasing radiogenic 40Ar by burial alteration, and at the same time acting as a support for the fundamental particles for the growth of authigenic fundamental particles that were found to incorporate Ar characterized by an excess of 40Ar.

RESERVOIR GEOMETRY OF FLUVIAL DISTRIBUTARY CHANNELS—IMPLICATIONS FOR NORTHWEST SHELF, AUSTRALIA, DELTAIC SUCCESSIONS

The exploration and development of stratigraphically trapped hydrocarbons requires detailed knowledge of the morphologies and reservoir characteristics of the stratigraphic body. Fluvial distributary channels are important exploration targets because they are typically isolated reservoirs, laterally and vertically sealed by delta plain and abandoned channel mudstone, and thus form excellent stratigraphic traps. The morphology and reservoir characteristics of fluvial distributary channels have been confused with fluvial channels in the past. Knowing the characteristics of fluvial distributary channels and their difference from fluvial channels is the key to the successful exploration and development of distributary channel reservoirs.Fluvial distributary channels, formed by mixed-load systems, are commonly rectilinear channel segments found only on the delta plain between the head of passes and the depositional mouthbars. While fluvial channel reservoirs are mainly sandstone deposits of meander pointbars or braided sheets, fluvial distributary channel reservoirs are typically elongated sandy channel sidebars attached to morphologically rectilinear channel walls. The sidebars form by both lateral and downstream accretion resulting from flow in a confined, but lowsinuosity thalweg, which may be filled with organic mud following channel abandonment. On 3D seismic data the morphology of a fluvial distributary channel is often slightly sinuous and can easily be mistaken for part of a meander channel belt.Fluvial distributary channels are usually thinner and shallower compared to their updip fluvial channel belts. Width-thickness ratios for fluvial distributary channel reservoirs are on average 50:1 (range 15:1 to 100:1), while meandering fluvial channel reservoirs have widththickness ratios typically >100:1, and braided river reservoirs show ratios of 500:1 or higher. Examples from the Mahakam Delta are used to illustrate these issues. Implications for exploration and development of deltaic deposits on the North West Shelf of Australia are discussed.

Micropaleontological investigations in the modern Mahakam delta, East Kalimantan (Indonesia)

The Mahakam delta is a mixed, fluvial and wave dominated delta located in the eastern part of the island of Borneo (the East Kalimantan province of Indonesia). The distribution of benthic fauna in this delta system is influenced by the combined or antagonistic action of three main parameters: fluvial input of fresh water and sediment, tide, and a strong regional north to south drift current. A model of the present-day faunal distribution has been established taking into account the perturbations induced by the tide and by the regional drift current. This model has been extrapolated into the recent past through the study of shallow cores that permit the reconstruction of late Holocene deltaic regression patterns.

Application of Rank( Sr), a maturity index based on chemical analyses of coals

The Rank( S r) classification of Suggate [NZ J. Geol. Geophys. 43 (2000) 521], which uses data from standard coal industry chemical analyses, is illustrated on interdependent diagrams with axes of atomic O/C and H/C and of calorific value and volatile matter. The Rank( S r) scale, which is compensated for coal type, is linear with depth under conditions of linear geothermal gradients, so that the depth value for each unit increase in rank depends on the geothermal gradient at the time of maximum temperature, normally that of maximum burial. A general relation is established between Rank( S r) and the temperature of attainment of rank: Temp.(°C)=10×Rank( S r)+15. Significant oil generation begins at Rank( S r) 9–10 and expulsion at Rank( S r) 11.5–12.5. A clear general relation exists between Rank( S r) and vitrinite reflectance, but Rank( S r) is somewhat more accurate over the range from peat to the end of the oil window. In the Paleogene Buller Coalfield, New Zealand, the use of Rank( S r) aids interpretation of the geological history. Coals in the Carboniferous Nottinghamshire-Yorkshire Coalfield in England probably contributed hydrocarbons, including oil, to the adjoining East Midlands hydrocarbon fields. Vertical and lateral variations in Rank( S r) in the coalfield, and the Rank( S r) values in Coal Measures at the base of the Permian, require a thick Mesozoic-Tertiary cover. In the oilfields of the Mahakam Delta, Indonesia, and the Taranaki Basin, New Zealand, Rank( S r)/depth gradients imply surface values that are close to zero where little or no cover has been eroded from above the wells, and inferred temperatures that are reasonably close to present temperatures.

Feasibility study on direct coal liquefaction in Indonesia

The distributions of steroidal and triterpenoidal alkanes and aromatic hydrocarbons and, where appropriate, triterpenoid alkenes and ketones, in nine oils, nine coals and three shales from the Mahakam Delta have been examined by gas chromatography-mass spectrometry. In all of the fractions there are high relative abundances of components of higher-plant origin, in keeping with the previous assignment of the organic matter in Mahakam sediments as type III. Comparison of molecular maturity measurements for the sediments and the oils extends earlier ideas that the source for the Handil oils must have a present depth of at least 3000 m. No major difference was observed here in the maturity (based on the molecular measurements) measured for coal-shale pairs with similar burial depths.In the oils, variations in the relative abundances of the monoaromatic steroid hydrocarbons relative to the triaromatic steroid hydrocarbons, taken with the results of earlier studies of the oils, have been ascribed tentatively to a migration effect.

ABSTRACT: Impact of an Evolving Geological Model on the Dramatic Increase of Gas Reserves in the Mahakam Delta: The Peciko Case History

ABSTRACT: Impact of an Evolving Geological Model on the Dramatic Increase of Gas Reserves in the Mahakam Delta: The Peciko Case History

ABSTRACT: Late Quaternary Stratigraphy and Sedimentology of the Offshore Mahakam Delta, East Kalimantan (Indonesia)

ABSTRACT: Late Quaternary Stratigraphy and Sedimentology of the Offshore Mahakam Delta, East Kalimantan (Indonesia)

Role of Polar Compounds as Source of Hydrocarbons and Reactive Medium during the Artificial Maturation of Mahakam Coal

To obtain a complete maturation set of strictly same precursor, an oil-prone tertiary coal from the Mahakam delta (Indonesia) is submitted to artificial maturation using confined pyrolysis. The analysis of the co-genetic phases (free hydrocarbons, resins, asphaltenes, and residual kerogen) reveals the composition and evolution of each fraction. It appears that the polars have a high oil potential and contribute significantly to the generation of hydrocarbons (up to 25% of the initial oil potential, and up to 50% at given maturation stages). During the main stage of bitumen generation, a great part of the initial oil potential is thus transferred to the polars. During the later stages of thermal breakdown, this potential is released and contributes to the generation of aliphatics. In addition to their contribution as hydrocarbon source, the polars of the Mahakam coal contain a significant amount of Dammar resin. This latter is revealed to be a source of hydronaphthalenics which are very efficient hydrogen ...

Laboratory Studies for Light-Oil Air Injection Projects: Potential Application in Handil Field

SummaryAir injection into light-oil reservoirs is now a proven field technique. Because of the unlimited availability and the nil access cost of the injectant, the application potential of this improved recovery process is promising when associated with the lack of available hydrocarbon gas sources for injection. One of the keys of a successful air injection project is the evaluation of the process by carrying out representative laboratory studies. Therefore, an original laboratory strategy was proposed to assess the recovery potential by air injection into light-oil reservoirs, and to help the determination and the quantification of optimal operating conditions.In this paper, the air injection technique applied to light-oil reservoirs is explained. Then, the laboratory strategy proposed for the evaluation of an air injection project is described, and the experimental objectives, devices, and procedures are explained. In order to provide reliable experimental data, high-pressure and high-temperature experiments (up to 40 MPa and 500°C) are performed with consolidated reservoir cores and reservoir oils, at representative conditions of the air injection process in light-oil reservoirs.Finally, a laboratory evaluation regarding a potential application for an air injection pilot in the Handil field (Mahakam delta, Indonesia) is presented and discussed.

Abstract: Differentiating depositional environments in the Mahakam Delta, East Kalimantan, using siliceous phytolith and diatom distributions

Abstract: Differentiating depositional environments in the Mahakam Delta, East Kalimantan, using siliceous phytolith and diatom distributions

ABSTRACT: A Comparison of Two Late Pleistocene Shelf Edge Deltas (Indonesia and Gulf of Mexico)--Stratigraphic Architecture, Systems Tracts, Bounding Surfaces, and Reservoir Potential

Abstract Thousands of kilometers of high-resolution seismic data have been collected over two late Pleistocene shelf-edge deltas in very different settings, the northern Gulf of Mexico and the eastern shelf of Borneo in Indonesia. Both deltas have been constructed by falling-to-lowstand deposition associated with the latest Pleistocene glacial maximum, the former by the temperate Mobile River, the latter by the equatorial Mahakam River. Four cores provide detailed stratigraphic control for the Mobile River delta while one long boring and numerous piston and vibracores provide stratigraphic control on the Mahakam delta. Systems tracts and key bounding surfaces have been related to the eustatic sea level curve in both settings over ca. 125 years. Sequence architectures differ significantly, an important consequence of different depositional settings. The tropical Mahakam shelf is tectonically active and has low wave energy, strong oceanic currents, upwelling, and a mixed siliciclastic - carbonate depositional system. The resulting falling-to-lowstand clinoforms downlap a highly irregular surface of isolated carbonate bioherms built above a transgressive surface that formed during the preceding sea level rise. The northeastern Gulf of Mexico is relatively stable, also has low wave energy, but is dominated by siliciclastic sedimentation. Falling-to-lowstand progradation of the Mobile River delta has occurred in numerous overlapping and spatially offset lobes incised by a complex channel network. Clinoforms downlap an isotope stage 5 interglacial condensed section. The Mobile depocenter has migrated from east to west; eastern lobes show evidence of wave reworking while the western flank is fluvially dominated. Both the Mahakam and Mobile deltas are composed of sand-rich clinoforms and channel deposits that possess excellent potential reservoir properties.

ABSTRACT: The areal control of building blocks of the third order depositional sequences in the Mahakam delta

ABSTRACT: The areal control of building blocks of the third order depositional sequences in the Mahakam delta

ABSTRACT: The Mahakam Delta, East Kalimantan, Indonesia as a model for the Oficina Formation, East Venezuela Basin

ABSTRACT: The Mahakam Delta, East Kalimantan, Indonesia as a model for the Oficina Formation, East Venezuela Basin

ABSTRACT: Reservoir facies of the Miocene Mahakam successions in the Kutei basin, east Kalimantan and their comparision with the modern Mahakam delta

ABSTRACT: Reservoir facies of the Miocene Mahakam successions in the Kutei basin, east Kalimantan and their comparision with the modern Mahakam delta