Published on March 9, 2014
Drilling Engineering 2 Course (2nd Ed.)
1. 2. 3. 4. General Notes Pore Pressure Prediction Abnormal vs. normal Pressure Fracture Gradient determination
Introduction The knowledge of the formations to penetrate, their strength properties as well as their behaviour when in contact with various drilling fluids is essential to properly plan and complete a successful drilling project. Parameters like pore pressure and formation strength determine aspects like: Choice of mud weight profile, Determination of casing setting depths, Design of optimal casing strings, Selection of the drill bit, Cementing additives and procedures. Spring14 H. AlamiNia Drilling Engineering 2 Course (2nd Ed.) 4
pressures as gradients The way how the formations react to drilling mud influences the selection of mud additives, borehole stability and therefore well control aspects. Within drilling, it is common to express pressures as gradients. With this concept, the hydrostatic pressure can be given as equivalent density which is independent of the depth and thus makes its comprehension and correlations of various concepts easier. Spring14 H. AlamiNia Drilling Engineering 2 Course (2nd Ed.) 5
reference depth On the other hand, when gradients are applied, it has to be always kept in mind that they are referred to a specific depth. Knowing this reference depth is essential to compute back the corresponding downhole pressures. Within drilling engineering, the drilling floor or rotary table (RKB) is the most often used reference depth. Geologists and geophysicists generally prefer to use their data in reference to ground floor or mean sea level (MSL). Spring14 H. AlamiNia Drilling Engineering 2 Course (2nd Ed.) 6
Geology Prediction Normally when a well is to be drilled, the drilling engineer is supplied from the geology department (or the geologist within the project team) with a sequence of predicted subsurface formations, their characteristics and markers, as well as knowledge about where special care has to be taken. Geologists draw this information from studying the local geology (deposition history), seismic mappings (2D or 3D surveys) and perform well to well correlations (geological maps). Whenever new information is gained (due to drilling and evaluation of a new well or further geophysical measurements) these maps are updated. Spring14 H. AlamiNia Drilling Engineering 2 Course (2nd Ed.) 7
Typical geological profile to plan a well Typical geological profile Spring14 H. AlamiNia Seismic record to determine the subsurface structure Drilling Engineering 2 Course (2nd Ed.) 8
local subsurface pressure regimes To understand the local subsurface pressure regimes, the geologic processes along with the depositional history and tectonic abnormalities have to be studied. When the well is located within shallow sediments that were laid down slowly within a deltaic depositional environment, the subsurface formation pressures can be assumed to be hydrostatic. Spring14 H. AlamiNia Drilling Engineering 2 Course (2nd Ed.) 10
Hydrostatic Pressure By definition, a hydrostatic pressure is developed due to the own weight of a fluid at a certain depth. This relationship is expressed as:
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1. Drilling Engineering 2 Course (2nd Ed.) 2. 1. Casing A. Review B. Setting Depths C. Connections D. API Casing Performance Properties . 3. 1.