What are the most effective methods for evaluating the quality of a reservoir?

One of the most popular methods is the logging method which utilizes tools to measure properties of the reservoir. Well logs, incudes gamma-ray, resistivity, neutron, and sonic logs. These logs aid in evaluating lithology, porosity, fluid content, offering valuable information about the reservoir. - Gamma-ray logs measures natural radioactivity to identify different rock types. - Resistivity logs indicates the rock’s ability to conduct electricity, helping differentiate between fluids and rock types. - Neutron logs measures the hydrogen content in the formation, aiding in porosity calculations. - Sonic logs provide information on rock density and comprehensive wave velocity, assisting in porosity and lithology determination.

Petrophysical analyses, including open-hole logging, sidewall and full-core analyses form the basis of the most effective techniques of reservoir evaluation. A complete picture of reservoir quality is found only when pressure and flow performance is also included. This consists of open-hole and cased hole techniques including drill-stem testing, flow testing and pressure transient testing. The end result of successful reservoir evaluation only comes to conclusion by the correct analyses and interpretation of all data acquired using the above techniques. This is through the teamwork of various people and companies. Once all the data interpretation done by the team is assembled, a total picture of the reservoir quality can be assured.

Logging has been my favorite means of establishing and understanding the subsurface reservoir for hydrocarbon. However, in the #oilandgasindustry, several methods are applied to ascertain effectively the quality of the reservoir rocks. For logging, the information of the subsurface which is recorded in a log is taken for examination, and a reasonable conclusion is drawn for decision making. For logging, several logs that are used to delineate the lithology, fluid content, type of hydrocarbon fluid, etc play an important role in the interpretation.

There are different types of logging services can help us to evaluate the reservoir. Conventional log can help us to identify the lithology, fluid type, porosity and good hydrocarbon intervals. Formation testers (MDT/RDT,..) help us to identify GOC and WOC, reservoir pressure, fluid type and its properties and also the permeability. Image log gives us information about bedding, dip and strike, recognizing different types of fractures in the formation, vugs and some features like stylolite From production logs we can find out the producing intervals, the fluid type from the producing intervals, the contribution of producing intervals in the production, leakage in the tubing, casing and cement plugs.

Logging methods, such as electrical and acoustic logging, use tools to see inside the Earth and figure out how much oil or gas is there and how easily it can be extracted.

The objective of core analysis is to reduce uncertainty in reservoir evaluation by providing data representative of the reservoir at in situ conditions. Core analysis techniques provide the premise to measure required petro-physical properties and to acquire simultaneously other reservoir rock dependent parameters. Core derived data have been integrated with other field data to minimize reservoir uncertainties that cannot be addressed by other data sources such as well logging, well testing or seismic.

It is also essential to understand the test and the reservoir complexity. SCAL and RCA could reduce uncertainty when no significant areal variations exist. Hence, for those discontinuous and unconventional reservoirs, we need to pay close attention to geologic interpretation and additional information that could help us reduce uncertainty. For example, from my experience, we rely on the SCAL and RCA evaluation results for a reservoir we initially considered to have areal continuity. Our surprise was that the sidetrack we drilled 60 ft away in one direction resulted in a dry well. Therefore, those tests could help to reduce uncertainty but could also help to increase uncertainty if we only use them for our evaluation.

Extracting core samples from the reservoir provides direct information about the rock properties as follows; - Porosity: core analysis help to determine the amount of pore space in the rock, which is critical for understanding how much fluid a reservoir can store - Permeability: core analysis provides insights into the rock’s ability to allow fluids to flow through, indicating how easily hydrocarbons can be extracted. - Saturation: core analysis estimates the amount of fluids present in the rock, distinguishing between oil, gas and water saturation.

Core analysis is a pivotal technique employed in reservoir characterization, leveraging samples extracted from the wellbore during drilling or coring operations to glean intricate insights into reservoir properties. This analysis comprises two main categories: routine core analysis (RCA) and special core analysis (SCAL). RCA entails measuring fundamental properties like grain density, bulk density, porosity, permeability, and fluid saturation through conventional laboratory methods. Conversely, SCAL delves deeper, assessing advanced properties such as relative permeability, capillary pressure, wettability, and rock-fluid interactions via specialized laboratory techniques.

Coring programs are usually conducted on exploration wells to understand the reservoir characteristics in new areas and on development wells for secondary/tertiary recovery studies. Core analysis operates at a more localized scale, focusing on specific intervals within the reservoir. While core samples provide detailed information about the rock properties in the sampled intervals, the coverage is limited to the sections where cores are obtained.

Best way to understand reservoir quality is through testing. PTA especially EWT give better understanding reservoir characteristics in terms of flow behaviour as well as possible inplace estimate especially for marginal fields. Compared to PTA, Cores and logs only provide vital information for rock characteristics though with limited in terms of radius of investigation. From the prospect of understanding techno-economic feasibility of marginal fields with limited data, testing dictates field future.

Well-testing is also carried out to know the efficiency of a well-stimulation operation carried out. This is done by knowing the skin factor before and after the well-testing operation is carried out. This gives an understanding of the reservoir deliverability.

Well testing is conducted for several essential purposes, including determining reservoir characteristics, estimating production rates, and identifying potential issues. One of the primary objectives is to evaluate the reservoir's deliverability and its ability to sustain production over time. This information is vital for reservoir engineers to plan for efficient extraction of hydrocarbons. Well testing involves collecting data on pressure, temperature, and fluid composition. This data is used to create pressure drawdown and buildup curves, which offer insights into reservoir properties. Reservoir Eng analyze this data?to estimate parameters like permeability, skin factor, and?reservoir pressure, which are crucial for reservoir modelung.

Testing methods utilizes tools to understand reservoir characteristics. They involve changing production rates and observing pressure responses to estimate reservoir properties. Some of the well testing technique include Drill Stem Test (DST) and Pressure Transient Analysis (PTA)

Based on my years of experience, i have realized that the quality of a reservoir determines the success of drilling operations. When porosity and permeability are high, there is better flow of fluid within the reservoir. This implies that assessing reservoir quality ensures efficient resource extraction and minimizes environmental risks.

One fascinating aspect of reservoir evaluation is its interdisciplinary nature, drawing upon expertise from geology, engineering, physics, and mathematics. This collaborative approach underscores the complexity and depth of understanding required to unlock the secrets hidden beneath the Earth's surface. Moreover, the continuous advancements in technology, such as AI, machine learning, and big data analytics, offer exciting opportunities to push the boundaries of reservoir evaluation further. By embracing innovation and interdisciplinary collaboration, we can delve deeper into reservoir characterization, unraveling its mysteries and maximizing its potential for sustainable energy production.

I think I've found it helpful to think systematically. As a reservoir engineer, thinking about systems when analyzing data from any reservoir is relevant. Reservoir engineers must use information from different disciplines and must have the ability to integrate it efficiently. We are blessed in our skills since we must think about how one action on the surface, one event in the geologic history, or a drastic change in reservoir conditions could impact a company's performance and bottom line.

The quality of a reservoir as defined by properties such as its hydrocarbon storage capacity and deliverability is most times accurately known at abandonment. Techniques such as well logging, core analysis and pressure testing informs a better understanding of the productivity of a reservoir before abandonment. Therefore, it’s advisable to use as much techniques as possible than relying on one or few to better describe a formation or it’s deliverability.