Unitization Consulting Services

Assessment of reserves, and providing unbiased opinion on oil and gas migration related issues associated with unitization in the leased area 


A&A Consulting Team of high-level and seasoned consultants has extensive experience in providing state-of-the-art consulting services to assess the reserves and give an unbiased opinion on oil and gas migration related issues associated with unitization in the leased area.


The oil & gas business, both onshore and offshore, is very capital intensive. Usually, several operators join hands, particularly when migration is evident on the basis of technical evidence and when there is need for secondary recovery methods to improve recovery. Even the most prolific reservoirs in the world face this problem due to agreement on blocks or boundaries, often created by allocations by national/federal/provincial/state governments.

The most amicable solution is unitization, which is carried out by experts on evaluating reserves and migration. Unitization is must for efficient drainage. It is the only technique to distribute revenue fairly amongst those incurring heavy operating and capital expenditure.


The commonly used methods in the oil & gas industry for determination of reserves or recoverable volumes are Volumetric, Decline, Material Balance, and Simulation methods. Although Decline method is most common, as it is the easiest, it is often subjective. Volumetric method gives in-place volumes, and reserves are based on assumed recovery factors based on producing drive mechanism. The reliability of Material Balance method is based on pressure and production/injection data. Fully built-up pressures are often not available. Besides, applicability of this method is limited only to the active or developed part of the reservoir. Simulation method, based on reservoir and well performance match on each phase, is the state-of-the-art and most dependable method for reliable reserves determination.

           Volumetric Method

This method requires well logs for determination of fluid saturations, porosities in the net pay zones, structure tops and fluid level contacts, if any. If core data are available, those provide excellent porosities, permeabilities, etc.

In the absence of laboratory PVT measurements, initial formation volume factors at original reservoir pressure are estimated by correlations. Area pertinent to the reservoir is an important parameter. It is possible to determine it if some fluid levels are determined on the basis of logs, RFT data, etc. In their absence, it is usually the section or block boundary. Usually detailed reservoir characterization, in terms of facies, layering, etc., is required.

Decline Method

This method of reserves determination requires accurate production data from each producer. Reliability obviously depends on duration of production history. Critical parameters for estimating reserves are extrapolations, which usually are subject to interpretation. This method ignores in-place volumes and recovery mechanism, and depends on the completions, stimulations, etc.

Material Balance Method

Accurate well bottom-hole pressures and production data on primary and secondary producing phases along with water production data at each time interval are essential. In order to organize these data on reservoir-wise basis, elaborate averaging techniques are used. Depending on the drive mechanism, calculations based on pertinent equations, this method provides reliable estimates of in-place and reserves only for the active part of the reservoir. Reliable PVT data, usually from laboratory measurements on reliable fluid samples, are required.

Simulation Method

When detailed reservoir description/characterization, in terms of facies, layering, etc., and production-pressure history of the reservoir are available, Simulation method, based on reservoir and well performance match on each phase, is the state-of-the-art and most dependable method for reliable reserves determination. 

A&A Consulting Team of high-level and seasoned consultants has the expertise and extensive experience in all commonly used methods (Volumetric, Decline, Material Balance, and Simulation) for determination of reserves or recoverable volumes of gas, gas-condensate/volatile oil, conventional oil, heavy oil, or extra heavy oil reservoirs, in sandstone or carbonate formations, located onshore or offshore, around the world.


Measured pressure and fluid level data are commonly used parameters to determine degree of communication or migration between blocks or boundaries. Usually there is significant pressure drop and change in fluid contact even without production due to communication with the producing part of the reservoir. If there is no or limited development or wells in the non-producing or less producing part, Simulation is the only reliable method to determine the impact of one on another.


Often, both in-place volumes and reserves are considered for unitization. Having determined the percentage partnership or ownership, reservoirs are developed for maximum recovery during primary and secondary recovery phases. Usually, parameters for unitization are agreed upon by arbitration, and all involved parties (companies) are committed till the depletion of reserves on full development of the reservoir.


A&A Consulting Team of high-level and seasoned consultants has the expertise and extensive experience in both domestic (U.S.) and international unitization projects (onshore and offshore). Some major examples are Norway’s Ekofisk (Argillaceous Sandstone), North Robertson Unit (Clearfork Carbonate), North East Pennwell Unit (San Andres Carbonate), West Brahenny (San Andres Carbonate), India’s KG Basin (Offshore Channel Sands), Cherokee Warpaty (Limestone Waterfloods in three phases). These are very prolific reservoirs and are being produced as per state-of-the-art technology. In each of these cases, phase-wise in-place, reserves were determined precisely on the basis of measured/observed field, well, and laboratory data. Elaborate analyses provided accurate interpretations to enable fair and acceptable unitization.


For over 25 years, we have built our worldwide reputation by providing practical solutions to complex problems, while adhering to the most rigorous standards of honesty and integrity, and delivering to our clients the highest quality of most innovative services with credibility, impartiality, fairness, objectivity, and equity.


A&A Consulting Team of high-level and seasoned consultants, with expertise and extensive experience in conducting state-of-the-art unitization studies is available to work on your company’s unitization projects, as well as represent your company in the Unitization Technical Committees, whenever requested.

In addition, we will be delighted to conduct customized training workshops on unitization, for the benefit of your company’s professionals and managers, at your company’s offices, around the world.

To put our high-level and seasoned consultants, subject matter experts (SME), to work on your company's unitization projects, around the world, please contact us.  



Contact: +1-281-359-2674 or send us an e-mail

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