Pressure Index (PI): A Novel Practical Method for Evaluating Pressure in Offshore Malaysia

Author(s):  
Y., E. Sugiharto

Pressure analysis is concerned with the study of systematic variations of reservoir pore pressure with depth. The most common interpretation for pressure analysis is pressure-depth plot analysis, but other techniques that magnify understated pressure differences are also available. Formation pressure measurement is of immense value in quantitative evaluation and risking of prospects. Once the pressure data has been acquired, we need to understand how to interpret the data received because reservoir pressure data has numerous applications and interpreting it wrongly could make the results misleading. At equilibrium state (i.e. there are no net forces, and no acceleration), a fluid in the system is called hydrostatic equilibrium. Hydrostatic pressure increases with depth measured from the surface due to the increasing weight of fluid exerting downward force from above. The traditional pressure evaluation is usually done in conventional unit such as psi, kPa, psi/feet, psi/m, kPa/m, ppg. The current work will introduce the concepts and definitions of formation pressure evaluation using Pressure Index (PI) with the unit g/cc. For better understanding of the application of PI, some reservoir studies are also discussed in this paper.

Author(s):  
A. O. Marnila

Geragai graben is located in the South Sumatera Basin. It was formed by mega sequence tectonic process with various stratigraphic sequence from land and marine sedimentation. One of the overpressure indication zones in the Geragai graben is in the Gumai Formation, where the sedimentation is dominated by fine grained sand and shale with low porosity and permeability. The aim of the study is to localize the overpressure zone and to analyze the overpressure mechanism on the Gumai Formation. The Eaton method was used to determine pore pressure value using wireline log data, pressure data (RFT/FIT), and well report. The significant reversal of sonic and porosity log is indicating an overpressure presence. The cross-plot analysis of velocity vs density and fluid type data from well reports were used to analyze the causes of overpressure in the Gumai Formation. The overpressure in Gumai Formation of Geragai graben is divided into two zones, they are in the upper level and lower level of the Gumai Formation. Low overpressure have occurred in the Upper Gumai Formation and mild overpressure on the Lower Gumai Formation. Based on the analyzed data, it could be predicted, that the overpressure mechanism in the Upper Gumai Formation might have been caused by a hydrocarbon buoyancy, whereas in the Lower Gumai Formation, might have been caused by disequilibrium compaction as a result of massive shale sequence.


2021 ◽  
Vol 7 (4) ◽  
pp. 46-63
Author(s):  
Dr. Faleh H. M. Almahdawi ◽  
Dr. Kareem A. Alwan ◽  
Ahmed K. H. Alhusseini

Prediction of formation pore pressure gradient is a very important factor in designingdrilling well program and it help to avoid many problems during drilling operations such as lostcirculation, kick, blowout and other problems.In this study, abnormal formation pressure is classified into two types; abnormal highpressure (HP) and abnormal low pressure (LP), therefore any pressure that is either above orbelow the hydrostatic pressure is referred to as an abnormal formation pressure.This study concerns with abnormal formation pressure distribution and their effect ondrilling operations in middle & south Iraqi oil fields. Abnormal formation pressure maps aredrawn depending upon drilling evidence and problems.Three formations are considered as abnormal formations in the region of study, theseformations geologically existed in Tertiary age and they from shallower to deeper are: LowerFars, Dammam and Umm Er Radhuma, Formations. The maps of this study referred to eitherhigh formations pressure such as (Lower Fars and Umm Er Radhuma) or the low formationspressure such as (Dammam) in middle and south of Iraq. Finally these maps also suggested andshowed the area, where no field is drill until now, which may behave as high, low and normalformation pressure for every formation understudy.


2011 ◽  
Vol 201-203 ◽  
pp. 399-403 ◽  
Author(s):  
Hong Qing Song ◽  
Ming Yue ◽  
Wei Yao Zhu ◽  
Dong Bo He ◽  
Huai Jian Yi

Porous media containing water is the prerequisite of existence of threshold pressure gradient (TPG) for gas flow. Based on theory of fluid mechanics in porous medium considering TPG, the non-Darcy flow mathematical model is established for formation pressure analysis of water-bearing tight gas reservoirs. It could provide semi-analytic solution of unsteady radial non-Darcy flow. According to the solution of unsteady radial non-Darcy flow, an easy and accurate calculation method for formation pressure analysis is presented. It can provide theoretical foundation for development design of water-bearing tight gas reservoirs. The analysis of calculation results demonstrates that the higher TPG is, the smaller formation pressure of water-bearing tight gas reservoirs spreads. In the same output, the reservoir sweep of non-Darcy gas flow is larger than that of non-Darcy liquid flow. And the pressure drop near wellbore is smaller than that of non-Darcy liquid flow, which is different from Darcy flow.


1973 ◽  
Vol 13 (1) ◽  
pp. 157
Author(s):  
F. H. Lepine ◽  
J. A. W. White

The accepted definition of an overpressured formation is one in which the pressure of the formation fluid is in excess of the theoretical hydrostatic pressure of the natural formation water if the formation water extended to surface. For the purposes of this paper, formations which have a pressure in excess of that corresponding to a gradient of 0.47 psi/ft from the surface to the depth of the formation are considered overpressured; this corresponds to the gradient of saturated saltwater. It is not necessary for a large reservoir to exist before drilling problems can be occasioned by abnormally pressured formations.Various means of determining the presence of overpressured formations exist and these formations have been encountered in many Australian basins including the Papuan Basin, the Bowen Basin, the offshore portion of the Carnarvon Basin, the Bonaparte Gulf Basin and in the Perth Basin. The usual means of combating abnormal pressures are by addition of barytes to the mud, by back pressure drilling or by allowing the formation pressure to partially deplete. This last alternative is only practical in low volume "shale-gas" occurrences. In the offshore Papuan Basin, a modified form of back pressure drilling known as the floating mud-cap technique was used for a productive reservoir containing a lengthy gas column.


2016 ◽  
Vol 34 (Supplement 1) ◽  
pp. e165
Author(s):  
Hsin-Ning Wang ◽  
Jiun-Jr Wang ◽  
Hao-Min Cheng ◽  
Chen-Huan Chen

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