Overview of Wire line Logging
What is meant by the terms Wire line logging? Logging can be defined as the systematic recording of data in wells being drilled or produced to obtain various characteristics of down hole formations. In other words, logging furnishes quantitative evaluation of hydrocarbons in place in formation. There are many different types of logs that can be run depending on the information desired. The different types of logs and the tools that are used to run them are covered later in the document.
Solutions Logging Provide
Formation evaluation is critical when making decisions about a well. Customers want to know accurate information regarding the formations they are drilling or completing.
Question customers ask include:
- What types of fluids are there?
- Where are these fluids?
- Are the zones porous?
- How thick are the zones?
- Are the zones permeable?
- What type of rock?
Logging answers these questions by providing a wealth of information on the rock and fluid properties of the formations penetrated including:
- Water saturation
- Types of hydrocarbons present and their mobility
- Rock and fluid samples
Accurately predicting the producibility of hydrocarbons found in place is achieved by analyzing the large amount of data sent uphole by logging tools. Research and development continues to improve the accuracy and reliability of logging tools available.
Basic Measurements and the Archie Equation
The basic measurements taken by logging tools in a wellbore are porosity and resistivity. Porosity is a measure of the total volume between the rock grains. Resistivity is the ability of a material to pass an electric current. The basic results gained by these measurements gives the fraction or percentage of the formation pore space that is occupied by water. This is known as water saturation. If the water saturation of a formation is known this tells us the amount of hydrocarbons because what is not water must be hydrocarbons. The basic measurements and result make up the Archie equation shown below.
The Archie Equation
The Archie equation is a convenient method of identifying fluid type in a clean formation. It requires the inputs of resistivity and porosity as well as other variables and exponents determined from core data or, where core data is lacking, by assumption. The resulting value of water saturation refers to the percentage of pore space that is occupied by water. Any remaining fraction of pore space not occupied by water will therefore be occupied by hydrocarbons. It is important to realize that while water saturation represents the percentage of water present in the pores of a formation, it does not imply a ratio of water to hydrocarbons that will be produced from a reservoir. The Archie equation simply provides us with the relative proportions of water and hydrocarbons contained within a reservoir. This equation was introduced by Gus Archie as a footnote in a 1942 publication, and has since become the foundation on which all logging technological and analytical innovations are built.
Open Hole Services
Openhole logging provides a continuous record vs. depth of many formation properties. Wireline logs record formation electrical resistivity, bulk density, natural and induced radioactivity, and hydrogen content. Measurements obtained are interpreted to give a continuous record versus depth for formation properties such as porosity, water saturation, and rock type.
PICO Technologies tools can be categorized into Induction Resistivity tools, Porosity/Lithology tools, Imaging tools, and specialty tools.
Induction Resistivity Tools
Induction Resistivity tools use electromagnetic signals to determine formation properties. This tool:
Porosity and lithology tools use properties of radiation and sonic signals to provide formation data. These tools include:
- PICO Telemetry Natural Gamma (PTNG)
- PICO Telemetry Spectral Gamma (PTSG)
- PICO Compensated Neutron Tool (PCNT)
- PICO Compensated Spectral Density Logging Tool (CSDL)
Future Projects and tools: “Link”
- Imagining tool
- Sonic Tool
- Dual Laterlog
- Formation Tester
2 1/4” Slim Triple Combo Tools
- Natural Gamma
- Spectral Gamma
- Thin Bed Array Induction