surface geology and subsurface geology
Post on 14-Jan-2017
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Mehran University Of Engineering Technology (SZAB) Campus
CONTENTS
1. Surface Geology2. Subsurface Geology 3. Well Cutting4. Coring5. Logging While Drilling6. Formation Testing7. Wireline Well-Logging Technique
Surface Geology
There are several areas to look for oil. The first is the obvious, on the surface of the ground. Oil and gas seeps are where the petroleum has migrated from its’ source through either porous beds, faults or springs and appears at the surface. Locating seeps at the surface was the primary method of exploration in the late 1800’s and before.
Subsurface Geology What is Subsurface Geology?
Subsurface geology is the study of the physical properties and location of rock and soil found below the ground surface.
• One of the most valuable reasons for learning about the subsurface is understanding the materials below man-made structures.
• These studies are commonly called geotechnical reports and are critical for building structures safely in areas with geologic hazards.
Well Cutting
Well samples are produced from drilling operations, by the drill bit penetrating the formation encountered in the subsurface.
Samples are taken at regular intervals. They are used to establish a lithologic record of the well and are plotted on a strip sample log.
Coring
One way to get more detailed samples of a formation is by coring, where formation sample is drilled out by means of special bit.
This sample can provide: Detailed lithological description. Porosity, permeability, fluid
saturation and grain density. These parameters are measured in
the laboratory and serve as a basis for calibrating the response of the porosity logging tools and to establish a porosity/permeability relationship.
Logging While Drilling
One of the major drawbacks of wireline information is that it is received several hours to several weeks after the borehole is drilled.
During this time period, the formation can undergo significant alteration, especially in its fluid saturation, effective porosity, and relative perm.
LWD allow wire line-type information to be available as near as real-time as possible.
Logging While Drilling (LWD) is a technique of conveying well logging tools into the well borehole down hole as part of the bottom hole assembly (BHA).
Logging While Drilling
Some available measurement in LWD technology: Gamma Ray Resistivity Density Neutron Sonic (fairly recent) Formation pressure Formation fluid sampler Borehole caliper (Ultra sonic azimuthal
caliper, and density caliper).
Formation Testing
Is a means of obtaining information concerning the liquid and pressure in an open-hole formations.
Three methods:■ Wire line testing■ Drill stem test (DST)■ Well Test Analysis
Methods of Formation Testing
Wire line testing:
Provide reservoir fluid samples, reservoir pressure, an indication of fluid mobility and information on reservoir continuity.
Drill stem Test:
A drill stem test (DST) is a procedure for isolating and testing the surrounding geological formation through the drill stem.
Well Test Analysis:
Two types of testing: pressure build-up and draw down test.
The primary objectives of well testing are to establish: Permeability thickness and permeability (K) Stratification (by sequential testing of layer). Well productivity. Investigate reservoir boundaries and size.
Wireline Well-Logging Techniques
Wireline logging involves the measurement of various properties of a formation including electrical resistivity, bulk density, natural and induced radioactivity, hydrogen content and elastic modulae.
These measurements may then be used to evaluate not only the physical and chemical properties of the formation itself, but also the properties of the fluids that the formation contains.
There are open hole logs and cased hole logs.
The open hole logs are recorded in the uncased portion of the wellbore. Cased hole logs are recorded in the completed or cased well.
There are measurements that can be made in both the open and cased holes and some that can only be made in open holes. Resistivity and density porosity are two examples of measurements that can be made in an open hole but not in a cased hole.
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