There are many complications associated with abnormally high fluid pressures in overpressured formations. Pore pressure can directly influence all parts of operations including drilling, geological studies, completion, and production. Accurate predictions of pore pressure and fracture pressure are vital aspects to the production and completion of safe, time efficient, and cost efficient projects. Knowledge of pressure distribution in the formation can greatly reduce complexities associated with drilling and completing a well. A three-method pore pressure and fracture pressure study was performed on two prospect deepwater wells located in the Gulf of Mexico. More than thirty offset wells in the greater region were initially analyzed for similarities with the two prospect wells. In the final analysis, only six wells were used to create pore pressure and fracture pressure models due to inconsistencies in similarities or lack of usable data in many of the offset wells. Pore pressure and fracture pressure models were constructed for the offset wells, and then applied and calibrated for the two prospect wells using drilling data such as mud weights, MDTs (Modular Dynamic Testing), and LOTs (Leak-off Test). Three types of pore pressure and fracture pressure models were used in the study: Eaton’s deep resistivity method; Eaton’s acoustic sonic method; and Bower’s interval seismic velocity method. Pore pressure and fracture pressure prediction was complicated by abnormal pressure in the formation due to undercompaction and seals. Both prospects were located in a deep subsalt environment. Low permeability and traps prevents fluid from escaping as rapidly as pore space compacts thus creating overpressure. Drilling through salt in deep water is expensive and risky. Elevated pore pressure and reduced fracture pressure underneath salt seals can create very tight mud weight windows and cause many drilling problems, as seen in the results of the offset wells’ pore pressure and fracture pressure models. Results indicate very small pore pressure and fracture pressure windows, or mud weight windows, because of overpressures in the formation caused by such a deep subsalt environment. Many casing points were needed in the final casing design of prospect wells to accommodate the smaller mud weight windows. Pore pressure has the most significant increase immediately below the salt, while the mud weight window remained constant or decreased with depth. The average mud weight window ranged between 1 to 2 pounds per gallon below the salt. / text

>Magister Scientiae - MSc / An accurate prediction of pore pressure is an essential in reducing the risk involved in a well or field life cycle. This has formed an integral part of routine work for exploration, development and exploitation team in the oil and gas industries. Several factors such as sediment compaction, overburden, lithology characteristic, hydrocarbon pressure and capillary entry pressure contribute significantly to the cause of overpressure. Hence, understanding the dynamics associated with the above factors will certainly reduce the risk involved in drilling and production. This study examined three deep water drilled wells GA-W1, GA-N1, and GA-AA1 of lower cretaceous Hauterivian to early Aptian age between 112 to 117.5 (MA) Southern Pletmos sub-basin, Bredasdorp basin offshore South Africa. The study aimed to determine the pore pressure prediction of the reservoir formation of the wells. Eaton’s resistivity and Sonic method are adopted using depth dependent normal compaction trendline (NCT) has been carried out for this study. The variation of the overburden gradient (OBG), the Effective stress, Fracture gradient (FG), Fracture pressure (FP), Pore pressure gradient (PPG) and the predicted pore pressure (PPP) have been studied for the selected wells. The overburden changes slightly as follow: 2.09g/cm3, 2.23g/cm3 and 2.24g/cm3 across the selected intervals depth of wells. The predicted pore pressure calculated for the intervals depth of selected wells GA-W1, GA-N1 and GA-AA1 also varies slightly down the depths as follow: 3,405 psi, 4,110 psi, 5,062 psi respectively. The overpressure zone and normal pressure zone were encountered in well GA-W1, while a normal pressure zone was experienced in both well GA-N1 and GA-AA1. In addition, the direct hydrocarbon indicator (DHI) was carried out by method of post-stack amplitude analysis seismic reflectors surface which was used to determine the hydrocarbon prospect zone of the wells from the seismic section. It majorly indicate the zones of thick hydrocarbon sand from the amplitude extraction grid map horizon reflectors at 13AT1 & 8AT1 and 8AT1 & 1AT1 of the well GA-W1, GA-N1 and GA-AA1 respectively. These are suggested to be the hydrocarbon prospect locations (wet-gas to Oil prone source) on the seismic section with fault trending along the horizons. No bright spot, flat spot and dim spot was observed except for some related pitfalls anomalies

Magister Scientiae - MSc / Pressure drop within a field can be attributed to several factors. Pressure drop occurs when fractional forces cause resistance to flowing fluid through a porous medium. In this thesis, the sciences of petrophysics and rock physics were employed to develop understanding of the physical processes that occurs in reservoirs. This study focussed on the physical properties of rock and fluid in order to provide understanding of the system and the mechanism controlling its behaviour. The change in production capacity of wells E-M 1, 2, 3, 4&5 prompted further research to find out why the there will be pressure drop from the suits of wells and which well was contributing to the drop in production pressure. The E-M wells are located in the Bredasdorp Basin and the reservoirs have trapping mechanisms of stratigraphical and structural systems in a moderate to good quality turbidite channel sandstone. The basin is predominantly an elongated north-west and south-east inherited channel from the synrift sub basin and was open to relatively free marine circulation. By the southwest the basin is enclose by southern Outeniqua basin and the Indian oceans. Sedimentation into the Bredasdorp basin thus occurred predominantly down the axis of the basin with main input direction from the west. Five wells were studied E-M1, E-M2, E-M3, E-M4, and E-M5 to identify which well is susceptible to flow within this group. Setting criteria for discriminator the result generated four well as meeting the criteria except for E-M1. The failure of E-M1 reservoir well interval was in consonant with result showed by evaluation from the log, pressure and rock physics analyses for E-M1.iv Various methods in rock physics were used to identify sediments and their conditions and by applying inverse modelling (elastic impedance) the interval properties were better reflected. Also elastic impedance proved to be an economical and quicker method in describing the lithology and depositional environment in the absence of seismic trace.