RESERVOIR CHARACTERIZATION AND PETROPHYSICAL PROPERTIES OF THE MIRI FORMATION (MIDDLE MIOCINE) MIRI, SARAWAK
| Presenter | : | HATEM S.A.ABIEDA |
| : | - | |
| Date | : | 6 / 1 / 2006 |
| Time | : | 3.00 PM |
| Venue | : | CONFERENCE ROOM, SCHOOL OF PHYSICS |
| Sypnosis | : | Rock successions outcropping around the Miri town, Sarawak, belonging to the Miri Formation (Middle Miocene strata) are the uplifted part of the oil bearing subsurface successions of the Miri oilfield. Data derived from outcrop studies concerning facies and sand body characteristics, and petrophysical properties are crucial for subsurface reservoir characterization and modeling of hydrocarbon reservoirs deposited in similar settings. Two main depositional environments have been recognized from the investigated outcrops, which are tide-dominated estuary and shallow marine settings. The tide-dominated estuary system of the Miri Formation has been interpreted as open-end tide-dominated estuary includes a variety of sub-environments; tidal channels and bars of estuary mouth, estuarine-upper flow regime sand flat, and restricted tidal flats. The estuarine succession has been interpreted to have been formed during an early transgressive event, representing the lower portion of the investigated Miri section. The shallow marine system varied from offshore transition, lower shoreface, lower-middle shoreface to middle-to-upper shoreface settings. Theses shallow marine deposits combined to form coarsening-upward, wave-and storm parasequence sets, which were formed during late transgressive event (offshore transition and lower shoreface) and relative sea-level stillstand and normal regressive event (lower-middle shoreface to middle-to-upper shoreface). Seven sandstone reservoir facies were recognized and characterized based on the integration of sedimentological and petrophysical data: three transgressive estuarine sandstones (trough cross-bedded shallow subtidal channel and bar sandstones of estuary mouth, parallel stratified upper flow regime sand flat, and massive sandstone of outer estuarine tempestites), two transgressive shallow marine sandstones (thin parallel stratified to hummocky cross-stratified offshore transitional sandstone and bioturbated lower shoreface sandstone) and two regressive shallow marine sandstones (thick amalgamated hummocky cross-stratified lower-middle shoreface sandstones and swaley cross-stratified middle-to-upper shoreface sandstones). The highest grade reservoir quality within the estuarine succession are represented by medium to fine grained and very well to well sorted tidal channels and bars sandstones and outer estuarine tempestites (>10 md and > 25 %). The fine grained, upper flow regime sand facies records an intermediate grade reservoir quality of 8.43 md and 24.5 % average. Reservoir quality within marine sandstone facies generally increases upward as depositional energy increases with a corresponding increase in textural maturity. The highest reservoir quality is found within aggradational to progradational interval, middle-to-upper shoreface facies, with high permeability (12.27-50.76 md) and high porosity (23.29-27.33 %). The lower-middle shoreface facies has shown an average grade reservoir quality (4.17 md and 25.69 %). Lower shoreface and offshore transition reservoir facies, which are finer grained and contain the higher proportion of clay, show the lowest grade reservoir quality among the shallow marine sandstones (1.28 md and 19.15 %). The most favorable reservoir facies of the Miri Formation were deposited in the higher-energy depositional environments associated with coarser, better sorted grains and low clay content. A decrease in depositional environment energy with a corresponding decrease in textural maturity and an increase in clay and bioturbation resulted in significant decrease in sandstones reservoir quality. |
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