Water Phase Salinity of Oil Based Mud

Water phase salinity is a factor showing the activity level of salt in oil based mud. In order to control the water phase salinity, salt is added into the drilling fluid. The salt added into the system will be dissolved by water in the mud; therefore, the chloride content will increase.

By increasing the chloride concentration (adding salt), the activity level in the mud will decrease. Salt is added in order to create an activity level which is equal to or less than formation water. Therefore, the water phase in the mud will not move into formation and cause a clay swelling issue. Practically, calcium chloride (CaCl2) or sodium chloride (NaCl) is the chemical to be used.

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Shell has started production from the world’s deepest offshore oil and gas project, the Stones development in the Gulf of Mexico

Shell has started production from the Stones development in the Gulf of Mexico, the world’s deepest offshore oil and gas project.

When fully ramped up at the end of 2017, the development is expected to produce approximately 50,000 barrels of oil equivalent per day (boepd), the company informed in a statement.

“Stones is the latest example of our leadership, capability and knowledge, which are key to profitably developing our global deep water resources. Our growing expertise in using such technologies in innovative ways will help us unlock more deep water resources around the world,” Royal Dutch Shell Upstream Director, Andy Brown, said.

The project, fully owned and operated by the supermajor, is Shell’s second producing field from the lower tertiary geologic frontier in the Gulf of Mexico.

According to the company, it features a more cost-effective well design, requiring less material and lower installation costs, which is expected to offer a US$1 billion (£749.38 million) reduction in well costs.

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Material Balance for a Water Drive Mechanism

This article will demonstrate a material balance equation in a natural water drive mechanism.  A full material balance equation is shown below:

Figure 1 - Full Material Balance Equation

Figure 1 – Full Material Balance Equation

Assumptions

  • Reservoir pressure above the bubble point (Pb). Above a bubble point, Rs = Rsi.
  • No water injection
  • No gas injection
  • No gas cap
  • Neglect formation and connate water compressibility (Cf and Cw have little effect for a gas cap drive mechanism.)
Figure 2 - Material Balance Equation with Assumption for a Natural Water Drive Mechanism

Figure 2 – Material Balance Equation with Assumption for a Natural Water Drive Mechanism

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Water Drive Reservoir

Some reservoirs have communication with a water zone (aquifer) underneath. When reservoir pressure drops due to production, the compressed water in an aquifer expands into a reservoir and it helps pressure maintenance. This mechanism is called “water drive”.

Water drive mechanism will be effective if an aquifer contacting reservoir is very large because water compressibility is very low. For example, an anticline structure with extensive water zone (aquifer) will have the most advantage from the use of a water drive mechanism. Conversely, stratigraphic reservoirs or highly-faulted reservoirs will have limited aquifer volume so water drive is insignificant.

Figure 1 - Water Drive Mechanism

Figure 1 – Water Drive Mechanism

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