Pore Pressure.docx

Pore Pressure Definition - What does Pore Pressure mean? Pore Pressure is the pressure of hydrocarbons within the pores of a hydrocarbon reservoir. Pore Pressure is at times the hydrostatic pressure which is exerted by the water column from the depth of a hydrocarbon formation up to the sea level. When the sediment rocks are compacted, the pore fluids are trapped inside and exert a tremendous amount of porous formation pressure.

Petropedia explains Pore Pressure Pore Pressure can be determined by the following methods: Equivalent Depth Method– This method assumes that to a certain depth, Pore Pressure is hydrostatic and rock sediments are normally compacted. A Normal Compaction Trend (NCT) is plotted from which Pore Pressure can be computed. The Ratio Method– In this method Pore Pressure is estimated by multiplying hydrostatic pore pressure by the ratio of measured depth value and normal depth value. Eaton’s Method– In this method Pore Pressure is estimated by expressing it to the equivalent densities. Resistivity method with NCT (Depth Dependent)– This method makes use of a relationship between measured resistivity and organic matter buried depth to estimate Pore Pressure along with plotting normal compaction trend for resistivity. Sonic method with NCT (Depth Dependent)– It makes use of the time taken by sonic waves in the formation having normal Pore Pressure. Effective Stress Method– This method makes use of plotting porosity versus depth curves, pressure versus depth curves and porosity versus Log Effective Stress to determine the Pore Pressure of the formation.

Hydrostatic Pressure Definition - What does Hydrostatic Pressure mean? Hydrostatic Pressure is the pressure of fluids present in a hydrocarbon reservoir. This pressure is usually exerted by a column of water on sea level from the depth of a hydrocarbon reservoir inside the earth's surface. The data collected from hydrocarbon and hydrostatic pressure is helpful in volumetric calculations. Hydrostatic pressure is also known as formation pressure or reservoir pressure.

Petropedia explains Hydrostatic Pressure In order to calculate hydrostatic pressure, bottom hole pressure measuring instruments are used to measure the fluid pressure in the pores of the reservoir. Usually, the pressure inside the reservoir keeps on changing when fluids are produced hence hydrostatic pressure is measured at a specific time and is referred to as initial reservoir pressure. When the fluids flow from the reservoir, the pressure distribution can be in a steady state flow, pseudo steady state flow or transient flow. Optical Fiber technology is considered to be advantageous in measuring the pressure and temperature of the reservoir.

Abnormal Pressure Definition - What does Abnormal Pressure mean? Abnormal Pressure is the fluid pressure of the reservoir pore which is different from the normal gradient pressure of saltwater. This pressure is linked with pressure which is higher than the normal pressure, the raised difficulty for well designer and raised risks of the well control problems. High pressure gradient of about ten pounds per gallon comparable to fluid density is considered to be abnormal. The pressure gradient below normal is known as subnormal. Abnormal Pressure can be found in various reservoirs which produce hydrocarbons.

Petropedia explains Abnormal Pressure Abnormal Pressure lies either below or above the normal pressure gradient and thus can be over pressured or subnormal. The mechanism that generates the Abnormal Pressure can be complicated and can vary from one region to another. The pressure is the hydrodynamic phenomena where time has a great role. All the Abnormal Pressure occurrences have limited lifespan and are directed by a continued presence of a cause for over pressure on one hand and by efficacy of seal on the other hand. These pressures are generated under the compacted regions as the shale matrix cannot support overburdened stress.

Fracture Pressure Definition - What does Fracture Pressure mean? Fracture pressure or formation fracture pressure is the pressure level, above which drilling fluids are capable of inducing rock formation fractures hydraulically. This pressure is considered in hydraulic fracturing which is a stimulating process that is done on routine basis on oil wells. A fracture pressure not only deforms a rock, but it is

‫‪powerful enough to etch the formations which results into fissures that are favorable for‬‬ ‫‪oil and gas to pass through. This pressure can be measured in gradient (psi/ft) or by‬‬ ‫‪fluid density equivalent, i.e., ppg.‬‬

‫‪Petropedia explains Fracture Pressure‬‬ ‫‪Fracture pressure is defined as the amount of pressure that is required to disintegrate a‬‬ ‫‪rock formation. This pressure is measured in gradient, i.e., psi/ft and it's helpful in‬‬ ‫‪determining whether or not the pressure would be enough to cause a fracture. When an‬‬ ‫‪oil well is deep, the fracture pressure gets increased due to the overburden pressure.‬‬ ‫‪Since deeply situated rock formations can be tough to fracture, the fracture pressure‬‬ ‫‪needs to be set really high to avoid the circulation problem or resistance from the rock.‬‬ ‫‪The pressure can vary at different depths and geological variations.‬‬ ‫نواع الضغوط ‪Types of pressur‬‬ ‫‪ \1‬الضغط الجوي‪Atmospheric pressure----‬‬ ‫ويعرف ضغط الجو بانه وزن عمود الهواء المسلط على نقطة معينة ويساوي تقريبا (‪)psi 14.7‬‬ ‫‪ \2‬الضغط الساكن الهيدروستاتيكي ‪Hydrostatic pressure----‬‬ ‫ويعرف الضغط الهيدروستاتيكي بانه الضغط الحاصل بسبب وزن عمود المائع (سائل او غاز )‬ ‫‪Hydrostatic pressure = Depth (True Vertical ) X Density‬‬ ‫‪Hp= TDV X p‬‬ ‫وتجدر االشارة هنا الى ان الضغط الهيدروستاتيكي يعتمد فقط على العمق الحقيقي الشاقولي وكثافة المائع فقط‬ ‫وبالتحويل الى الوحدات الحقلية فان معادلة الضغط الهيدروستاتيكي تكون على الشكل االتي ‪---‬‬ ‫‪Hydrostatic pressure psi = Density in ppg X0.052 X True Vert . Depth ft‬‬ ‫مالحظة‪press . Gerad . psi ----‬‬ ‫= ‪)X Density of mud (ppg 0.052‬‬ ‫‪ \4‬ضغط التكوين ‪Formation pressure‬‬ ‫ويمكن تعريفه بانه ضغط المائع الموجودة في داخل مسامات التكوين (‪)Of formation pore spaces‬‬ ‫ويمكن القول بان ضغط المسامات او ضغط التكوين طبيعي عندما يكون سببه الضغط الهيدروستاتيكي للماء المحصور في التكوين أي في‬ ‫المسامات التكوين والتي يوجد ترابط بينهما وبين الضغط الجوي‬ ‫وعند تقسيم هذا الضغط (ضغط ماء مسامات التكوين ) على العمق الشاقولي الحقيقي يعطي مقدار تدرج ضغط المائع في التكوين وهو عادة يكون‬ ‫محصور بين ‪psi \ft 0.465-0.0433‬‬ ‫عند غياب المعلومات الحقيقية حول طبقة ماء يمكن اعتماد قيمة تدرج ضغط المائع في التكوين تساوي‬ ‫(‪ ) o.465 psi \ ft‬وهي تمثل مقدار تدرج الضغط في خليج المكسيك‬ ‫‪ \5‬ضغط الطبقة الطبيعي ‪Normal formation pressure‬‬ ‫ان ضغط التكوين الطبيعي مساوي الى الضغط الهيدروستاتيكي لماء التكوين والممتد من السطح الى ما تحت التكوين وعليه فان تدرج الضغط في‬ ‫نقطة يجب ان يكون مساوي الى تدرج ضغط ماء التكوين المصاحب لمسامات التكوين التحت السطحية‬ ‫أ\ طرديا بنسبة تركيز االجزاء الصلبة الذائبة مثل االمالح ‪Salts dissolved solids like‬‬ ‫ب\ عكسيابكمية الغازات في ماء التكوين‬ ‫‪ \6‬ضغط الطبقة الغير طبيعي ‪Abnor mal formation pressure‬‬ ‫ويمكن تعريفه بانه أي ضغط مسامي يكون يكون اعلى من الضغط الهيدروستاتيكي لماء التكوين المصاحب لمسامات التكوين احيانا يسمى ب‬ ‫‪ Geo pressure‬او ‪Over pressure‬‬ ‫‪Ahmedwod Ahmednman Arb‬‬ ‫شكرا ع المعلمات القيمة في الصفحة واود ان اضيف ع هذه القالة بانه هناك ضغط اخ هو ضغط التكسير للطبقة ‪ Fracture pressure‬وهو الضط‬ ‫الذي تبدأ عنده الطبقة بالتشقق وتتقبل دخول المائع اليها‪ ،‬ويجب ان ﻻيصله الضغط الهيدروستاتيكي لعمود المائع في البئر ﻻنه عندها تتشقق الطبقة‬ ‫وتحدث مشكلة الفقدان للمائع او سائل الحفر‪.‬‬ ‫مﻻ حظة ‪ :‬ان الضغط الستاتيكي يجب ان اكبر من ضغط التكوين للسيطرة عليه ومنع حدوث اﻻنفجار واقل من ضغط التكسير لضمان عدم تشقق الطبقة‬ ‫وحدوث مشكلة الفقدان وشكر‬