All points of the earth's crust are subjected to a stress state in perfect static equilibrium. In the rock also prevails a pore pressure, that of the fluid filling the porous space. When drilling a well, the forces previously supported by the removed rock are redistributed at the well periphery where a stress concentration occurs. To balance this stress concentration and avoid rock failure, the well is filled with a drilling mud which pressurises the well bore wall. The minimum mud density required to ensure well stability is called the Critical Stability Density. It depends on numerous parameters (...) Read More >

A well is not only a “safety barrier” to protect surface installations and operators from the uncontrolled flow of flammable (oil), explosive (gas) and toxic (i.e. H2S) fluids. It is also an “environmental barrier” protecting drinking water aquifers or any other sensitive level from the content of the well during drilling (drilling mud), hydraulic fracturing (fracturing fluid) and production (oil, gas and production water). Properly managing well integrity first requires the relevant monitoring (baseline and continuous monitoring during development and production) of all water sources (aquifer and (...)  Read More >

When a low cohesive rock is put on stream there is a high risk that solid grains are removed from the payzone and transported with the fluid to the surface. Such a process requires two main conditions. First following stress and pore pressure variations resulting from depletion, the rock damages in the vicinity of the well. This damaging phase is a necessary but insufficient condition for the well to produce solid particles. Movements of solids are triggered by hydrodynamic forces which basically depend on the fluid velocity. Therefore, this mobilisation of grains occurs almost exclusively at (...)  Read More >

Corrosion is a physico-chemical deterioration process due to the interaction of a material with its surrounding environment. Corrosion can be concentrated locally to form a pit or crack but it can also extend across a wide area to produce macroscopic failure. Although most alloys corrode, some metals are more intrinsically resistant to corrosion than others, either due to their fundamental atomic nature or due to the way in which reaction products form. Some dedicated metals such as zinc, magnesium, and cadmium have naturally slow reaction kinetics. Gold nuggets do not corrode (...)  Read More >

Unlike oil, gas is highly volatile and, consequently extremely difficult to transport. Therefore the most conventional way to valorize gas is to supply a close regional/local heating/electricity market. When it comes to valorize remote gas accumulations in uninhabited regions (steppes Amazon rainforest, arctic regions) located very far from potential markets, gas transportation becomes the key factor. Over reasonable on-shore distances of a few hundred to a few thousand kilometers, the gas can be regularly re-compressed and transported by pipeline being. However, over greater distances (...)  Read More >

The well is the “connection tool” between reservoir and surface. For obvious reasons linked to the lack of homogeneity of both the rock type (from soft shale to hard sandstone or limestone) and the pore pressure regime, it cannot be drilled in a single phase. 

A well is built as a telescopic structure with its diameter reduced in stages (typically 20 inches at the surface and 6 inches at the reservoir level) and covered by successive cemented casings then completed by a tubing in which the multiphasic effluent (mixture of oil, water and gas) (...)  Read More >

The reservoir rock is built through conventional consolidation and diagenesis processes. Coarse sediments (sands or lime grains) saturated by sea water are deposited on the sea bed then progressively buried and loaded by overlying sediments. Following this loading process, grains compact, porosity decreases and, as water is expelled, pore pressure increases either with a normal pressure gradient (pressure equal to the weight of the hydrostatic column) or sometimes with an abnormal gradient (pressure greater than hydrostatic pressure) when water cannot (...)  Read More >

April 2015 – Let us speak Deep Offshore

Up until the mid-80s, offshore developments were limited to oil or gas fields that lay under no more than 400m of water. As was the case for conventional offshore at the end of the 60s, the emergence of deep offshore was justified by the progressive decrease in the potential of conventional offshore and by the increasing demand from emerging countries. The high price of the barrel at the beginning of the 90s, in particular after the Gulf War, forced operators to develop what appeared to be a new “black gold mine”. (...)  Read More >

February 2015 – Let us speak Drilling

"If you can’t get to the oil, let the oil get to you” would be a succinct way of describing the beginnings of oil production. Hydrocarbons that form deep in the subsurface and do not meet any traps, migrate to the surface and then seep through rocky outcrops, produced the first oil fields. The shores of the Caspian Sea are thought to be the cradle of the oil industry because, during the IXth century, oil is thought to have been produced in the Baku region of Azerbaijan. Marco Polo who visited the Azerbaijani capital in 1264 described “seepages from which oil flows abundantly” (...)  Read More >