Hi Zainab,

For new fields, some prefer to consider 5-spot, 7-spot, or 9-spot well distributions.

However, the best way is to consider optimization techniques if you use flow simulation to evaluate the reservoir performance. More specifically, you can determine the optimal number and locations of productiona and injection wells.

For the WAG process, determining the optimal production/injection rates and other operational variables can also be optimized through various optimization algorithms.

Let me know if you need detailed info about these topics.

Best,

Watheq

Injection wells are classified by the U.S. Environmental Protection Agency into six classes according to the type of fluid they inject and where the fluid is injected, as follows:

Class I wells: inject hazardous and non-hazardous wastes below the lowermost underground source of drinking water (USDW). Injection occurs into deep, isolated rock formations that are separated from the lowermost USDW by layers of impermeable clay and rock.

Class II wells: inject fluids associated with oil and natural gas production operations. Most of the injected fluid is brine that is produced when oil and gas are extracted from the earth.

Class III wells: inject super-heated steam, water, or other fluids into formations to extract minerals. The injected fluids are then pumped to the surface and the minerals in solution are extracted. Generally, the fluid is treated and re-injected into the same formation.

Class IV wells: inject hazardous or radioactive wastes into underground sources of drinking water. These wells are banned under the Underground Injection Control (UIC) program because they directly threaten public health.

Class V wells: are injection wells that are not included in the other 4 classes. Some Class V wells are wastewater disposal wells used by the geothermal industry, but most are wells such as septic systems and cesspools. Generally, they are shallow and depend upon gravity to drain or "inject" liquid waste into the ground.

Class VI wells: inject carbon dioxide (CO2) into deep underground subsurface rock formations for long-term storage, or geologic sequestration. The number of wells will depend on the magnitud of the reservoir, the type of thereservoir, the size of the reservoir, the resources available for drilling, among other factors. The maximu production and injection rate will also depend on the type of reservoir, the location of the reservoir, the cost associated to the extraction of the energy source from the reservoir, the resources available, the public opinion, the energy need of the countries, among others.

How Many Injection Wells Are Used in Oil and Gas Operations In California? About 52,000 injection wells are used for waterflood, steamflood, cyclic steam, and water disposal. These wells are referred to as Class II injection wells in the Underground Injection Control (UIC) program. Where Are They? Injection wells are found in many oil and gas fields located in the counties where oil and gas are produced.

What Are They For? Class II injection wells are used to safely dispose of the salt and fresh water produced with oil and gas. Injection is often accomplished in a manner that will increase oil and gas production. About 15 times more water than oil is produced from California's oil and gas fields.

Does Injected Water Serve a Useful Purpose? Yes. In more than 95 percent of the Class II injection wells, water is injected into petroleum reservoirs to increase oil production. About 60 percent of California's oil production is a result of Class II injection wells

Is Anything Besides Water Injected? Current state and federal regulations allow nonhazardous fluids produced from oil or gas wells and several other nonhazardous fluids associated with the production process to be injected into a Class II well. These other fluids include diatomaceous earth-filter backwash, thermally enhanced oil recovery cogeneration plant fluid, water-softener regeneration brine, air scrubber waste, drilling mud filtrate, naturally occurring radioactive materials (NORM), slurrified crude-oil, saturated soils, and tank bottoms. What Is An Injection Well Like? After a well is drilled, sometimes to depths over 5,000 feet, steel pipe called casing is cemented in the hole. The casing and cement prevent fluids in different zones from mixing with each other or with injected fluids. The casing and cement are perforated opposite the injection zone. To provide an extra layer of protection, tubing is placed in the well to a point just above the perforations and a packer is used near the bottom of the tubing to seal it against the casing. The packer prevents water from entering the space between the tubing and casing when water is injected down the tubing. Several tests are run to make sure the well is operating properly and the injected fluids are confined to the intended injection zone, and repeated on a periodic schedule.

What Is An Injection Zone Like? An injection zone is usually sandstone, a rock porous and permeable enough to accept injected fluids. Rock beds chosen for injection zones are covered by impermeable beds, like shale, that act as cap rocks, confining injected liquids in the porous beds.

How Is Produced Water Handled? After oil and gas are separated from the produced water at the producing well, the water is piped or trucked to the injection site. There, the water is transferred to holding tanks and filtered and pumped down a Class II injection well.

How Often Are Injection Wells Checked? All injection wells are monitored by Division engineers to ensure the wells are operated properly and have mechanical integrity. Monitoring includes reviewing operational data and running tests like Mechanical Integrity Tests (i.e., spinner, temperature, and pressure tests and tracer surveys). In addition, most well sites are inspected annually by Division engineers. Samples of the injected fluids may be taken at any time to confirm compliance.

How Are Injection Wells Permitted? Operators of Class II injection wells must file for a permit with the Division. Before a permit is issued, the proposed injection project is studied by Division engineers and reviewed by the appropriate Regional Water Quality Control Board. Division engineers evaluate the geologic and engineering information, solicit public comments, and may hold a public hearing, if necessary. Injection project permits include many conditions, such as approved injection zones, allowable injection pressures, and testing requirements.

Are Injection Wells Safe? Yes. Class II injection wells provide a viable and safe method to enhance oil and gas production and dispose of produced fluids and other fluids associated with oil- and gas-production operations. In California, Class II injection wells have an outstanding record for environmental protection. A peer review conducted by a national organization, the Ground Water Protection Council, found the Division has an excellent program that effectively protects underground sources of drinking water.

Firstly, in order to effectively design your reservoir development strategy, some parameters must be determined either through geological data or data obtained from exploratory or wildcat wells. Reservoir properties such as permeability, porosity, fluid (oil, water and gas) saturation, thickness etc. must be estimated. With these relevant data, you can estimate the type of production strategy you need, conduct economical analysis among others.

In addition, these data will also be useful in implementing the type of well patterns most suitable for the field. The attached file contains detailed information on classes of well pattern.