Oil and gas reservoir protection during the process of drilling, completion and development in oil and gas fields.Introduction:A petroleum reservoir or oil and gas reservoir is a subsurface pool of hydrocarbons contained in porous or fractured rock formations. Petroleum companies extract crude oil from the Earth using a perforation in the Earth’s surface called an oil well. Crude oil is a liquid form of petroleum. In addition, wells provide natural gas. Oil wells are 5 to 36 inches in diameter.
The drill bit breaks through the ground and drilling fluid brings the cuttings to the surface. Completing the well includes adding perforated casing in the production zone for the oil to flow into the well. But unfortunately its not going that simple way, usually we face problems during the oil and gas excavating process. So the scientists have been working so hard to find the problems involved while excavating the oil and gas and they tried hard to define those problems and solve it or avoid it at all.
One of those problems is the reservoir damage.Reservoir damageProducing formation damage has been defined as the impairment of the unseen by the inevitable, causing an unknown reduction in the unquantifiable. In a different context, formation damage is defined as the impairment to reservoir (reduced production) caused by wellbore fluids used during drilling/completion and workover operations. It is a zone of reduced permeability within the vicinity of the wellbore (skin) as a result of foreign-fluid invasion into the reservoir rock. Typically, any unintended impedance to the flow of fluids into or out of a wellbore is referred to as formation damage. This broad definition includes flow restrictions caused by a reduction in permeability in the near-wellbore region, changes in relative permeability to the hydrocarbon phase, and unintended flow restrictions in the completion itself. Flow restrictions in the tubing or those imposed by the well partially penetrating a reservoir or other aspects of the completion geometry are not included in this definition because, although they may impede flow, they either have been put in place by design to serve a specific purpose or do not show up in typical measures of formation damage such as skin. After we know what is the reservoir damage the most important thing is to know how to avoid it so that we can protect our reservoir then we can excavate as much hydraucarbon as we can from the oil and gas producing formation.From the well study of the reservoir damage we noticed that the main reasons that can cause the reservoir damage is the fluids used while drilling the well or while the well compeletion process, in the next few paragraphs we ar going to talk about the drilling fluids and compeletion fluids what is it and how it can affect the reservoir and can cause its damage.Drilling FluidsThe drilling-fluid system”commonly known as the “mud system””is the single component of the well-construction process that remains in contact with the wellbore throughout the entire drilling operation. Drilling-fluid systems are designed and formulated to perform efficiently under expected wellbore conditions. Advances in drilling-fluid technology have made it possible to implement a cost-effective, fit-for-purpose system for each interval in the well-construction process.The active drilling-fluid system comprises a volume of fluid that is pumped with specially designed mud pumps from the surface pits, through the drillstring exiting at the bit, up the annular space in the wellbore, and back to the surface for solids removal and maintenance treatments as needed. The capacity of the surface system usually is determined by the rig size, and rig selection is determined by the well design. For example, the active drilling-fluid volume on a deepwater well might be several thousand barrels. Much of that volume is required to fill the long drilling riser that connects the rig floor to the seafloor. By contrast, a shallow well on land might only require a few hundred barrels of fluid to reach its objective.A properly designed and maintained drilling fluid performs several essential functions during well construction: – Cleans the hole by transporting drilled cuttings to the surface, where they can be mechanically removed from the fluid before it is recirculated downhole.- Balances or overcomes formation pressures in the wellbore to minimize the risk of well-control issues.- Supports and stabilizes the walls of the wellbore until casing can be set and cemented or openhole-completion equipment can be installed.- Prevents or minimizes damage to the producing formation(s).- Cools and lubricates the drillstring and bit.- Transmits hydraulic horsepower to the bit.- Allows information about the producing formation(s) to be retrieved through cuttings analysis, logging-while-drilling data, and wireline logs.The cost of the drilling fluid averages 10% of the total tangible costs of well construction; however, drilling-fluid performance can affect overall well-construction costs in several ways. A correctly formulated and well-maintained drilling system can contribute to cost containment throughout the drilling operation by enhancing the rate of penetration (ROP), protecting the reservoir from unnecessary damage, minimizing the potential for loss of circulation, stabilizing the wellbore during static intervals, and helping the operator remain in compliance with environmental and safety regulations. Many drilling-fluid systems can be reused from well to well, thereby reducing waste volumes and costs incurred for building new mud.To the extent possible, the drilling-fluid system should help preserve the productive potential of the hydrocarbon-bearing zone(s). Minimizing fluid and solids invasion into the zones of interest is critical to achieving desired productivity rates. The drilling fluid also should comply with established health, safety, and environmental (HSE) requirements so that personnel are not endangered and environmentally sensitive areas are protected from contamination. Drilling-fluid companies work closely with oil-and-gas operating companies to attain these mutual goals.