Acidizing is a stimulation method of pumping acid in the formation. Pumping acid into the limestone, carbonate, or dolomite formations tends to partially dissolve the rock and increase its permeability. The type of stimulation fluid, volume, sequence of fluids, and rate of pumping are carefully calculated based on formation properties and test flow parameters to get the best results.

Difference between Stimulation and Fracturing

Acid Fracturing is the process of forcing acid treatment into the formation with pressures higher than formation fracture pressure. Acid fracturing is used in Carbonate formation and is intended to either go beyond the damage zone or for creating long conductive channels extending deeper into the reservoir.

Difference between Stimulation and Fracturing

Acid Wash is the process of pumping acid into tubular or wellbore with the objective of cleaning. It is not intended for any treatment of the formation but only to clean any possible debris that might be restricting the flow of formation fluid into the wellbore.

Difference between Stimulation and Fracturing

Cavity effect refers to the effect of having a cavity in the shaped charges. Experiments indicated that flat explosive surface were not effective in achieving good penetration. When the surface was made with conical cavity, greater penetration was achieved. Experiments also revealed that having a conical liner as the front of cavity creates deeper perforations. Ability of shaped charges to perforate deeper into the metal and rock with conical cavity shape is termed as cavity effect.

Detonating cord is a part of perforation set up. It is connected to detonator on one end and to the shaped charges of the perforation gun on the other. It is a means of transferring detonation from detonator to the shaped charges. Cord consists of high explosive core covered with plastic or lead jacket. It can have either round or rectangular cross section. Detonating cords are defined by grains per foot (gpf) which is a unit of explosive load per unit length. One pound contains 7,000 grains. Round detonators usually have 70 to 80 gpf.

Extreme Overbalance Perforation is a method of perforating a well by applying a very high pressure surge to the formation. Pressure surges are designed to overcome fracture initiation pressure and break down each perforation tunnel with a very short fractures. Extreme Overbalance Perforation approach has been found to be a more effective technique than overbalance or underbalance perforations for water injection wells.

Once the perforation guns are at depth, the string is filled with small amount of liquid (brine, acid, solvent or frac fluid) at top of the gun. Rest of the string is filled with compressed gas (Nitrogen) before initiating the perforation sequence. On detonation, liquid is driven into the perforation at very high rate due to rapid expansion of gas and initiates fractures to extend effective wellbore radius.

Fracturing is also commonly known as 'Hydraulic Fracturing'. It is used in formations with very low permeability or on wells where the formation is badly damaged. Fluid is pumped into the formation with surface pressure high enough to break it open and propagate the fracture. Fractures propagate beyond near wellbore damage and connect the well to the reservoir fluid enhancing the rate of flow of fluid into the well.

Difference between Stimulation and Fracturing

Matrix Acidizing is the stimulation process in which acid treatment is injected into the formation but below fracture pressure. It can be used in Carbonate as well as Sandstone formations. In Sandstone formations, the primary objective of 'Matrix Acidization' is to remove any particles plugging the formation that can be removed by acid and hence increase the flow of formation fluid into the wellbore.

Difference between Stimulation and Fracturing

Overbalance perforation is the process of perforating the well with hydrostatic pressure inside the casing or liner more than the reservoir pressure. Overbalance perforation ensures maintaining complete control on the well. However it risks causing formation damage as the wellbore fluid tends to flow into the reservoir through the perforation tunnel.

The overflush is the fluid stage of the stimulation treatment cycle that is pumped after pumping the main treatment fluid. Normally a weak acid or brine is used as an overflush fluid. When the main treatment fluid, which is normally a mixture of Hydrofluoric and Hydrochloric or organic acids, comes in contact with the formation, it could produce some byproducts. The objective of overflush is to displace the main treatment acid and also to flush out any byproducts or non-reacted mud chemicals out of the wellbore after the culmination of the treatment cycle.

Perforation is the process of piercing holes through casing, cement and formation at selected intervals. The objective is to provide a flow path for the formation fluid to the wellbore. Perforation guns loaded with explosives are run in hole either on wireline or on drill pipe and activated across the identified zone.

Stimulation treatment contains multiple fluids that are pumped in sequence to achieve the best results. Preflush is the fluid stage that is pumped before the main treatment. Preflush is used for dissolving calcareous materials, rust, or displacing brine before the main treatment fluid comes in contact with the formation. The presence of these materials could cause the plugging of formation pores when coming in contact with the main treatment fluid. The composition is decided based on the type of reservoir rock and formation damage.

Primer is a part of shaped charges used for perforating casing and formation. It provides a link between detonating cord and the main charge. Primer contains same charges as that of main charges but is more sensitive.

Proppants are the solid materials used in 'Hydraulic Fracturing'. In hydraulic fracturing, the cracks are opened by pumping fluid into the well with high surface pressure. Since the cracks are opened by force, they tend to close as soon as pressure is removed. Proppants are the solid particles that enter into the crack and don't allow them to close. Materials like sand, bauxite, ceramic and some lighter weight materials are usually used as proppants.

Selective Firing System is a perforating switch technology that utilizes unique switch identification logic to selectively perforate multiple intervals in a single trip. Digital communication is used to operationally check and arm the switches. The system uses series of micro-processors with unique addresses and can be checked from surface. In case of a misfire, that device can be skipped to go to the next device.

Shaped charges are used as part of testing and completion operations for perforating casing and formation. The charges are loaded on perforation gun and are lowered into the well either through wireline or drill pipe. Once on perforation depth, the charges are detonated through a detonating cord. The perforating jet formed as a result of explosion, penetrates the casing and deep into the formation. This creates a tunnel for reservoir fluid to flow into the well.

Shaped charges have four main parts; outer casing, premier charge, main charge and conical liner. Outer casing is the metal body that holds all other parts together. Ceramic or glass are also used as casing material. Premier charge provides the link between the detonating cord and the main charge. Liner is a cone shaped solid or powdered metalic layer that collapses under detonation pressure allowing the formation of perforating jet.

Simulation is the process of enhancing the production from the reservoir. Once the well is perforated, it is tested to ascertain the production rate from the reservoir by recording parameters like pressure, temperature, flow rate, etc. Depending on the type of reservoir and its properties, appropriate methods are adopted to enhance the flow rate.

Stimulation methods used for enhancing well production could be mechanical, chemical, or a combination of the two. Fracturing & Acidizing are the two commonly used methods for enhancing productivity. Fracturing is performed above the fracture pressure of reservoir formation, whereas acidizing or matrix treatment is performed below the fracture pressure of the reservoir. Fracturing is aimed at creating new highly conductive flow paths whereas matrix treatment aims at restoring the natural permeability of the reservoir rock by clearing near wellbore damage.

Difference between Stimulation and Fracturing

Once the well is drilled to the target depth and production casing / liner has been run, the well is perforated across the zone of interest for either testing or producing reservoir fluid. The term 'Tunnel' refers to the part of the perforation hole created by perforation guns in casing and cement. Part of the hole that extends into the formation is referred as 'Cavity'.

Underbalance perforation is the process of perforating the well with hydrostatic pressure inside the casing or liner less than the reservoir pressure. This has a distinct advantage that soon after the perforation, reservoir fluid tends to flow into the wellbore. In the opposite scenario of pressure inside casing or line being more than reservoir pressure, the wellbore fluid tends to flow into the perforation tunnel and could damage the reservoir.

Perforating underbalance without appropriate pressure control equipment has a risk of developing into a well control situation. When using Tubing Conveyed Perforation (TCP), it is possible to reduce the hydrostatic pressure inside tubing by displacing part of the tubing to lighter fluid or Nitrogen before perforation. Pressure can be safely contained and observed on surface soon after perforation.

Wormhole refer to the conductive channel created in the formation as a result of acidization. As the acid forces its way into the formation, it tends to dissolve part of the matrix in the pore spaces, creating permanent void channel that can connect to the reservoir fluid beyond the near wellbore region. The reservoir fluid then is able to flow easily into the wellbore through these conduits.