The modern reservoir management process involves goal setting, planning, implementing, monitoring, evaluating, and revising plans.

The modern reservoir management process involves establishing a purpose or strategy and developing a plan, implementing and monitoring to plan, and evaluating the results. None of the components of reservoir management is independent of others. Integration of all these is essential for successful reservoir management.

The most important aspect of reservoir management deals with the strategies for depleting the reservoir to recover petroleum by primary and applicable secondary and enhanced oil recovery methods.

Development and depletion strategies will depend upon the reservoir ‘s life stage. In case of a new discovery, we need to address the question of how to best develop the field (well spacing, number of wells, recovery schemes, primary, and subsequently secondary and tertiary).

1. Data Acquisition, Analysis and Management:

Reservoir management starting from developing a plan, implementing the plan, monitoring and evaluating the performance of the reservoir requires a knowledge of the reservoir that should be gained through an integrated data acquisition and analysis program. Data analyses require a great deal of effort, scrutiny, and innovation. The key steps are:

Plan, justify, time, and prioritize.
Collect and analyze.
Validate /store (data base).

An enormous of data are collected and analyzed during the life of a reservoir. An efficient data management program-consisting of collecting, analyzing, storing and retrieving -is needed for sound reservoir management. It poses a great challenge.

Throughout the life of a reservoir, from exploration to abandonment, an enormous amount of data is collected. An efficient data management program consisting of acquisition, analysis, validating, storing, and retrieving plays a key role in reservoir management. It requires planning, justifying, prioritizing, and timing

Data Types:

The types of data collected before and after production are shown in table lists the data under the various broad classification including the timing of acquisition and analyses. It is emphasized that the multidisciplinary professionals need to work as an integrated team to develop and implement an efficient data management program.

Classification	Data	Acquisition Timing	Responsibility
Seismic	Structure, stratigraphy, faults, bed thickness, fluids, interwell heterogeneity	Exploration	Seismologists, Geophysicists
Geological	Depositional environnement, Diagenesis, lithology, Structure, faults, and fractures	Exploration, Discovery & development	Exploration &development geologists
Logging	Depth, lithology, thickness, porosity, fluid saturation, gas/oil, water/oil and gas /water contacts, and well-to-well correlations	Drilling	Geologists, petrophysicists and engineers
Coring	Routine analysis: depth, lithology, thickness, porosity, permeability, and residual fluid saturation SCAL: Relative permeability, capillary pressure, pore compressibility, grain size, and pore size distribution.	Drilling	Geologists, drilling and reservoir engineers, and laboratory analysts
Fluid	Formation volume factors, compressibilities, viscosities, Gas solubilities, chemical, compositions, phase behavior, and specific gravities	Discovery, delineation, development, and production	Reservoir engineers and laboratory analysts
Well Test	Reservoir pressure, effective permeability, thickness, stratification, reservoir continuity, presence of fractures or faults, productivity and injectivity, indices, and residual oil saturation	Discovery, delineation, development, production and injection	Reservoir and production engineers
Production & Injection	Oil, water, and gas production rates, and cumulative productions, gas and water injection rates and cumulative injections, and injection and production profiles	Production & injection	Production & reservoir engineers

Data acquisition and Analysis:

Multidisciplinary groups (geophysicists, geologists, petrophysicists, drilling, reservoir, production and facilities engineers) are involved in collecting various types of data throughout the life of a reservoir. Land and legal professionals also contribute to the data collection process. Most of the data, except for the production and injection data, are collected during delineation and development of the fields.

An effective data acquisition and analysis program requires careful planning and well -coordinated team efforts of interdisciplinary geoscientists and engineers throughout the life of the reservoir. On one hand, there may be the temptation to collect lots of data; and on the other hand, there may be the temptation to short -cut data acquisition to reduce costs. Justification, priority, timelines, quality, and cost-effectiveness in data acquisition should be the guiding factors in data acquisition and analysis. It will be more effective to justify to management data collection if the need for the data, the costs , and benefits are clearly defined .

Certain types of data such as core derived information, initial fluid properties, fluid contacts, and initial reservoir pressure can only be obtained at an early development stage . Coring , logging , and initial reservoir fluid sampling should be made at appropriate times using the proper procedure and analyses . Normally, all wells are logged; however , an adequate number of wells should be cored to validate the log data .Initial bottom -hole pressure measurements should be made , preferably at each well and at selected “key wells “ perdiocally . Key wells represent 25% of the total wells. It is beneficial to measure pressures in all wells at least every two to three years to aid in calibrating reservoir models.

It is essential to establish the specification of what and how much data need to be gathered and the procedure and frequency to be followed .

DATA VALIDATION:

Field data are subjected to many errors (sampling, systematic, random, etc.). Therefore, the collected data need to be carefully reviewed and checked for accuracy as well as for consistency.

In order to assess validity , core and logs analyses data should be carefully correlated and their frequency distributions made to identify different geologic facies .Log data should be carefully calibrated using core data for porosity and saturation distributions , net sand determination , and geological zonation of the reservoir .The reservoir fluid properties can be validated by using the equation of state calculations and empirical correlations .The reasonableness of geological maps should be established by using the knowledge of depositional environment. The presence of faults and flow discontinuities as evidenced in a geological study can be investigated and validated by pressure interference and pulse and tracer tests.

DATA STORING AND RETRIEVAL:

The reconciled and validated data from the various sources need to be stored in a common computer database accessible to all interdisciplinary end users. As new geoscience and engineering data are available, the database will require updating. The stored data are used to carry out multipurpose reservoir management functions including monitoring and evaluating the reservoir performance.

DATA APPLICATION:

A better representation of the reservoir is made from 3D seismic information. The cross- well tomography provides interwell heterogeneity.

Geological maps such as gross and net pay thickness, porosity, permeability, saturation, structure, and cross-section are prepared from seismic, core and log analysis data. These maps, which also include faults, oil -water, gas -water and gas-oil contacts, are used for reservoir delineation, reservoir characterisation, well locations, an estimate of original oil and gas in place.

The more commonly used logging systems are:

· Open Hole Logs:

- Resistivity, Induction, Spontaneous Potential, Gamma ray,

- Density, Sonic Compensated Neutron, Sidewall neutron

- Porosity, Dielectric, and Caliper.

· Cased Hole Logs:

- Gamma ray, Neutron (except SNP, Carbon /Oxygen, Chlorine, Pulsed Neutron and caliper.

The well log data that provide the basic information needed for reservoir characterization are used for mapping, perforations, estimates of original oil and gas in place, and evaluation of reservoir perforation.

Production logs can be used to identify remaining oil saturation in undeveloped zones in existing production and injection wells. Time-lapse logs in observation wells can detect saturation changes and fluid contact movement. Also, log -inject -log can be useful for measuring residual oil saturation.

Core analysis is classified into conventional, whole-core, and sidewall analyses. The most commonly used conventional or plug analysis Involves the use of a plug or relatively small sample of the core to represent an interval of the formation to be tested. Whole core analysis involves the use of most of the core containing fractures, vugs, or erratic porosity development. Sidewall core analysis employs cores recovered by sidewall coring techniques.

Unlike log analysis, core analysis gives direct measurement of the formation properties, and the core data are used for calibrating well log data . These data can have a major impact on the estimates of hydrocarbon in place, production rates, and ultimate recovery.

The fluid properties are determined in the laboratories using equilibrium flash or differential liberation tests. The fluid samples can be either subsurface sample or a recombination of surface samples from separators and stock tanks. Fluid properties can be also estimates by using correlations.

Fluid data are used for volumetric estimates of reservoir oil and gas in place, reservoir type, (oil, gas, or gas condensate), and reservoir performance analysis. Fluid properties are also needed for estimating reservoir performance, wellbore hydraulics, and flowline pressure losses.

The well test data are very useful for reservoir characterization and reservoir performance evaluation. Pressure build-up or falloff tests provide the best estimate of the effective permeability -thickness of the reservoir in addition to reservoir pressure, stratification, and presence of faults and fractures. Pressure interference and pulse tests provide reservoir continuity and barrier information. Multiwell tracer tests used in waterflood and in enhanced oil recovery projects give the preferred flow paths between the injectors and producers. Single well tracer tests are used to determine residual oil saturation in waterflood reservoirs. Repeat formation tests can measure pressure in stratified reservoirs indicating a varying degree of depletion in the various zones.

Production and injection data are needed for reservoir performance evaluation.

General Geological Activities in Reservoir Description and Input from Engineering Studies.

Geologist Skills

Sunday, February 2, 2025

Reservoir Management Process: