Reservoir
Reservoir is a rock formation that is capable of containing oil, gas or water. To be able to produce and be commercially viable, the reservoir should be thick and vast. It should have required porosity and permeability to be able to accumulate and flow the reservoir fluid. Sandstone and Carbonates are most common conventional reservoir rocks.
Quaternary
Quaternary is the most recent geological period and falls under Cenozoic era. Quaternary period stated around 0.5 million years ago.
Pyroclastic Sediments
Unlike Terrigenous Sediments (Clastic), which are derived from land, Pyroclastic Sediments are derived from volcanic eruptions. They may closely resemble the Terrigenous Sediments, for they may have gone through similar weathering and abrasion cycle after falling above the existing sediments as a result of eruptions.
Precambrian
Precambrian is the oldest geological era. The life on earth started in ocean sometime in Precambrian era and spread to land sometime in Devonian period.
Paleozoic
Paleozoic is a geological era that started around 550 +/- 50 million years ago. Paleozoic era is subdivided into 7 different periods. These subdivided periods in reverse chronological order from oldest to latest are Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian and Permian.
Evaporites
Evaporites are sediments which include salt minerals like Anhydrite, Gypsum, Halite etc. Evaporites however are not deposited through sedimentary cycle like other sedimentary rocks but through the precipitation sequence from brine. Evaporites are usually found in thick beds and form good cap rock for oil and gas entrapment.
Devonian
Devonian is a period within Palezoic geological era. In geological time scale, Devonian period started around 350 +/- 50 million years ago and lasted for about 50 million years. Devonian period is considered significant since the life is thought to have spread from ocean to land during this period.
Cretaceous
Cretaceous is the period of Mesozoic geological era. In geological time scale, Cretaceous period started around 135 +/- 5 million years ago and lasted for about 65 million years.
Clay
Clay is a clastic with very fine particles having diameters less than 0.004 mm. It's chemical name is a 'hydrous platy aluminosilicate' and is the finest grade of clastic minerals. Clays are further sub-divided in five different groups based on chemical and physical characteristics as Kaolinite, Illite, Smectite, chlorite and Glauconite.
Wall Hook Guide
Wall Hook Guide is also used if the hole size is much larger than the size of the fish. It has a long opening on the side. The longer opening helps in bringing the fish to the center of the tool even if the guide passes alongside the top of the fish.
Taper Tap
Taper tap is an internal catching fishing tool. It has a simple taper mandrel with hardened teeth on it. It is used in situations where there isn't enough annular clearance to catch the fish externally. The tap is run inside the fish top. Slow rotation while lowering the string cuts threads inside the fish body and helps in engaging it to the tap.
Spiral Grapple
Spiral grapple has a helical spring type shape. It is installed into an Overshot Bowl. It has wickers on the inside to catch the fish and tapered helical spirals on the outside that match with the helical spiral on the inside of the Bowl. Spear grapple is used for swallowing and catching the fish from outside.
Spear
Spear is used for internally catching the tubular fish. Spear has a mandrel, grapple, release ring and nut. The mandrel has a tapered helix. Grapple has a matching surface. Turing left moves the mandrel down and places the grapple in engaged position. Grapple expands due to helical wedge surface on the mandrel and grips the fish from inside. For releasing, the spear is bumped down and turned to the right. This tends to move the grapple down and place it in release position.
Oversize Guide
If the size of the hole is much greater than the fish size, there is a possibility that a standard guide may pass the top of the fish without guiding it to the centre of the overshot. In that case running an oversize guide has greater chances of success in catching the fish.
The guide is run below the overshot assembly. With string rotation, it scoops the fish to the centre of the hole and helps the grapple in overshot swallow the top to engage and retrieve it.
Overshot
Overshot is a fishing tool for catching the fish externally. Most overshots have primarily three parts. Top sub, bowl and guide. Top sub has connection for the running string. Bowl houses packer, spiral grapple and spiral grapple control. Guide directs the tool on top of fish. Packer is a rubber ring.
As the overshot moves down over the fish, the rubber provides a sealing around fish making it possible to pump drilling fluid down the fish and to circulate it under pressure outside of the stuck fish. Bowl has tapered helical spiral on the inside. Grapple has identical tapered helical spiral on the outside.
Grapple control keeps the grapple into its place. The tool is slowly rotated close to top of fish. As the guide washes over the top of the fish and brings it inside the overshot, the top of the fish is swallowed by the grapple. A slow upward pull tends to move the grapple down. The helical wedges on the inside of the bowl make the grapple to contract and grip the fish tightly.