Core Cluster South Sudan

19/02/2024

Interpreting logs in the oil and gas industry is a crucial process for understanding the characteristics of subsurface formations and making informed decisions about exploration, drilling, and production. Various types of well logs provide valuable information about the rock formations, fluid content, and other properties encountered in a wellbore. Here are some key types of well logs and how they are interpreted:
Gamma Ray Log (GR): This log measures the natural gamma radiation emitted by the formations. It helps identify lithology changes and stratigraphic variations. High gamma readings can indicate shale, while low readings may indicate clean sandstone or limestone.
Resistivity Logs: Different types of resistivity logs (e.g., Deep, Medium, Shallow) measure the electrical resistivity of the formations. Low resistivity indicates fluid-filled formations (hydrocarbons or water), while high resistivity indicates more resistive rocks like shale or anhydrite.
Spontaneous Potential Log (SP): SP measures the natural electrical potential difference between the formation and the drilling mud. It can indicate permeable zones and help identify fluid contacts.
Porosity Logs: Neutron and density logs are used to estimate formation porosity. Neutron logs measure the hydrogen content (related to porosity), while density logs measure bulk density. Porosity is crucial for estimating reservoir storage capacity.
Sonic Log (DT): Sonic logs measure the travel time of sound waves through the formation. These logs help calculate formation rock velocity and aid in determining porosity, lithology, and mechanical rock properties.
Caliper Log: The caliper log measures the diameter of the borehole. Variations in borehole size can affect other log measurements and may indicate unstable formations.
Formation Pressure Logs: These logs, including pressure-while-drilling (PWD) and pressure-while-tripping (PWT), help assess formation pressure gradients, which are crucial for well control and drilling safety.
Petrophysical Analysis: Integrating and analyzing multiple log measurements can help determine rock and fluid properties, such as porosity, water saturation, permeability, and hydrocarbon content. Petrophysical software and techniques are used for this purpose.
Cross-Plotting: Log data can be plotted against each other to identify trends and relationships, aiding in lithology and fluid identification. For instance, a neutron-density cross-plot can help distinguish different lithologies.
Core Data Integration
Interpreting logs requires expertise and an understanding of geological and reservoir engineering principles. Oil and gas companies typically employ petrophysicists and geoscientists who specialize in log interpretation to make informed decisions about reservoir potential, drilling strategies, and production optimization.

15/09/2023

13/09/2023

World's largest lithium deposit been identified in the southern half of the caldera at Thacker Pass and immediately to the north in the Montana Mountains.

23/08/2023

𝗥𝗲𝘀𝗲𝗿𝘃𝗼𝗶𝗿 𝗖𝗼𝗺𝗽𝗮𝗿𝘁𝗺𝗲𝗻𝘁𝗮𝗹𝗶𝘇𝗮𝘁𝗶𝗼𝗻 𝗗𝗲𝘁𝗲𝗿𝗺𝗶𝗻𝗮𝘁𝗶𝗼𝗻:

One of the main reasons why reservoir compartmentalization determination is important is its impact on reservoir management decisions. Compartments may have differing fluid saturations, permeability, and pressure behavior. Failure to identify and analyze these compartments accurately can lead to inefficient well placement and development strategies. By understanding the compartmentalization, reservoir engineers can make informed decisions regarding well location, completion design, and recovery mechanisms. This knowledge helps maximize production and reduce costs associated with ineffective drilling operations.

Another significant aspect of determining reservoir compartmentalization is the understanding of fluid flow dynamics within the reservoir. Compartments can have barriers or faults that restrict the movement of fluids between them. Identifying these barriers is vital for estimating the total volume of hydrocarbons in place, as well as predicting fluid migration patterns. Accurate knowledge of compartmentalization aids in optimizing well spacing and improving recovery efficiencies. It also helps reduce the risk of water or gas breakthrough, which can negatively impact production rates.

Several techniques and technologies are available to determine reservoir compartmentalization. Traditional methods include analyzing well test data, pressure transient analysis, and production logging. These techniques provide valuable information about pressure differentials, fluid saturations, and connectivity between different zones. Advanced technologies such as seismic imaging and 4D reservoir modeling have revolutionized compartmentalization determination. Seismic surveys help identify subsurface structures and fault systems that can influence fluid flow. 4D reservoir modeling combines seismic data with reservoir engineering data to create a dynamic representation of the reservoir, giving insight into its compartmentalization and behavior over time.

Integrated reservoir studies using a combination of these techniques are often employed to obtain a comprehensive understanding of reservoir compartmentalization. This multidisciplinary approach allows for a more accurate depiction of the reservoir's internal architecture and connectivity between compartments. Identification of compartments can be further enhanced by incorporating geochemical and petrophysical data, as well as core analysis results.




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22/08/2023

Functions of drilling mud in oil and gas wells

Drilling mud, also known as drilling fluid, serves various functions in oil and gas wells, including:

1. Cooling and lubrication: Drilling generates a lot of heat and friction, which can cause damage to the drilling equipment and create risks of fire and explosions. Drilling mud helps cool and lubricate the drilling bit and shaft to prevent overheating, reduce wear and tear, and ensure efficient drilling.

2. Wellbore stability: Drilling mud helps maintain the stability of the wellbore by preventing the formation of cracks or holes that can cause loss of drilling fluid or collapse of the well walls. The mud creates a hydrostatic pressure that counteracts the pressure of the formation fluids, keeping the wellbore intact.

3. Cuttings removal: Drilling produces cuttings or small rock fragments that need to be removed from the wellbore to prevent clogging and facilitate further drilling. Drilling mud carries the cuttings to the surface where they can be separated and disposed of.

4. Formation evaluation: Drilling mud helps to identify the properties of the formation being drilled. The mud carries rock fragments and formation fluids to the surface, where they can be analyzed to determine the presence of hydrocarbons, formation pressure, permeability, and other important parameters.

5. Well control: Drilling mud plays a crucial role in well control by balancing the pressure of the formation fluids and preventing blowouts or uncontrolled releases of fluids. The mud weight and composition are carefully regulated to maintain a safe and stable well environment.

Overall, drilling mud is essential for the successful drilling and completion of oil and gas wells, ensuring safety, efficiency, and optimal production.

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14/08/2023

13/08/2023

launches the industry’s highest-pull wireline conveyance system
has launched the MaxPull high-pull conveyance system that can pull from 18,000 pound-force to 30,000 lbs in wells 12,192 meters deep or more. The MaxPull system’s engineered integration of wireline conveyance components brings efficiency, reliability, and sticking avoidance to complex well trajectories that were not previously wireline accessible, the company said.
“With the industry’s highest-pull wireline conveyance system, drillers can expect drill pipe-free wireline operations in any with vertical well efficiency and minimum sticking ,” said Hinda Gharbi, president, of Wireline, Schlumberger. “In addition, our customers can mitigate operational risk and save time during comprehensive data acquisition by eliminating the use of conventional conveyance.”
The MaxPull system can pull up to 30,000-lbs line tension, which is 43 percent higher than previously possible. Pairing the system with wireline tractors further improves well access in complex well trajectories while minimizing the number of logging runs. The system has been tested in a wide variety of well environments and trajectories in the Middle East, Europe, Asia, West Africa, and North and South America.
A customer deployed the MaxPull 30000 system in the Gulf of Mexico well where job modeling indicated tension of 20,900 lbf. The existing highest-pull system of 21,000 lbs did not provide an overpull capability in the event of tool sticking. By using the MaxPull 30000 system, the customer had a margin of 9,000 lbf of additional pull. A sticking incident occurred during a reservoir fluid sampling station. A pull in excess of 29,300 lbs was applied to free the tool string, avoiding a four-day operation and the loss of valuable fluid data, and saving more than $3 million, according to Schlumberger.




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09/08/2023

Faults and Folds and Why they are Form

Faults and folds are geological structures that are formed due to tectonic forces acting on rocks. These structures may cause changes in the Earth's surface, leading to mountain building, earthquakes, and other significant geological events.

Faults are fractures or cracks in rock formations along which there has been movement. There are three main types of faults: normal, reverse, and strike-slip. Normal faults occur when rocks move away from each other, as the crust stretches. Reverse faults are formed when rock layers are pushed together, causing one rock layer to move over another. Strike-slip faults occur when rocks move horizontally past one another.

Folds happen when rock layers curve, bend, or curve due to pressure from tectonic plates. Folds can be classified as anticlines (upward-arching folds) or synclines (downward-arching folds). Folds can also be classified as symmetrical (mirror images of one another) or asymmetrical (one side of the fold is steeper than the other).

Both faults and folds are formed due to the movement of tectonic plates. The plates move due to the convection currents in the Earth's mantle. When these plates collide or move apart, they cause pressure on the rocks, which can lead to the formation of faults and folds. These structures can have a significant impact on the geological features of an area, as well as the potential hazards that may be associated with them.

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25/07/2023

What Is Hydraulic Fracturing?
Hydraulic fracturing commonly referred to as “fracking,” is a well stimulation technique used in the extraction of trapped natural gas and oil from “unconventional” low permeability rock formations such as shale or coal beds. Small detonations and explosions and the injection of large volumes of pressurized fracturing fluid (a mix of water, particulates, and a variety of other chemicals) deep underground create or re-open cracks or fissures in the rock increasing the volumes of fossil fuel that can be recovered. The process also generates and has to safely manage, the huge volumes of flow back fluid made up of naturally occurring formation brines together with the returned fracturing fluid. Wells can be drilled vertically for hundreds of meters and then horizontally for up to around 3 km to increase the exposure to the fuel reservoir. This combination of horizontal drilling and well stimulation is referred to as unconventional oil and gas development (UOGD) although the media and the public tend to use the term “fracking” to describe the whole process; Figs. 1 and 2 show stylized graphics comparing conventional and unconventional gas extraction processes and a more detailed cross-section of an unconventional site respectively. While there is no such thing as a standard UOGD site and each development will vary in terms of capacity, intensity, and potential impact, a fracking episode can require millions of gallons of fracturing fluid and each well can be hydraulically fractured multiple times during its operational life. Although hydraulic fracturing has been used since the 1940s it has only relatively recently been used at scale. This, together with the re-engineering of extraction techniques and development of new technologies including directional drilling and intensive clustering of wells, has made the significant amounts of gas in low permeability formations including shale and coal seams increasingly commercially accessible. In the United States, where the process is most intensively used, unconventional extraction generated 67% of marketed gas in 2015 whereas as recently as 2010 most natural gas was produced from “conventional” deposits in porous rock such as sandstone through natural pressure and pumping operations.




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25/07/2023

Source Rock Deposition

Depositional environments favouring the accumulation of source rocks are illustrated in Figure A in the context of a section through a plate. The amount of kerogen present in sediments is a balance between bioproductivity, survival, and dilution by inorganic grains. To take some extremes: Low productivity—Aeolian (wind-blown) desert sandstones where land plant growth is restricted due to the extremely arid environment.
High productivity—Areas of ocean upwelling where the enhanced supply of nutrients fuels explosive growth of phyto- and zooplankton.
Poor survival—Chalk composed almost exclusively of coccolith skeletal debris (high bioproductivity) but where all the coccolith body tissues are destroyed by bacterial activity under strongly oxic open marine conditions.
Excellent survival—Early rifting phases of oceans where both optimum sedimentation rates and anoxic conditions of the lakes and enclosed seaways promote high rates of organic matter preservation.
Strong dilution—The prolific sediment supply of major deltas produces organic lean delta-front and pro-delta sediments despite high bioproductivity.
Minimal dilution—Coals where the lignocellulosic and other tissues of high-productivity land plants are well preserved in a delta-top environment starved of (or bypassed by) mineral grains.
As illustrated above, the aspects of the depositional environment favouring organic preservation are anoxia and elevated sedimentation rates, though excessive sedimentation rates will eventually lead to dilution.
As implied in Figure A, organic matter falling to the ocean or lake floor has to pass through various zones of bacterial degradation (Figure 😎. The normal open-water oxic bacterial community is highly effective at destroying oil-prone organic matter, so time spent in this zone has disastrous effects on potential oil source rocks. These conditions are found in the water column and surface sediments in the open ocean, but in strongly stratified basins (e.g., the present-day Black Sea) only the top of the water column may be oxic.
Thus to summarize (Figure C), the optimum oil-prone source rocks are deposited where anoxia develops in an aqueous environment enjoying high rates of sedimentation. The combination of high rates and oxic environments favours the accumulation of gas-prone source rocks such as coals.
(C. Cornford, in Encyclopedia of Geology, 2005)




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19/07/2023

DECLINE CURVE ANALYSIS

Advantages of Decline Curve Analysis:
- Easy to do
- Based on measured data
- Accepted methods for reserve determination
- Often sufficiently adequate for financial or other purposes
- Integral part of many economical evaluation applications.

Disadvantages of Decline Curve Analysis:
- Assumes that whether controlled the curve shape in the past will continue to do so in the future.
- Decline shapes vary with the reservoir type, drive mechanism and maturity of production.
- Decline shapes are often applied inappropriately.




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