The Quad Neutron is a nuclear measuring tool that uses four (4) independent detectors specially designed for the evaluation of formations through pipes. Two (2) Neutron-Neutron detectors (NN) and two Neutron-Gamma detectors (NG) allow to extract the response of the reservoirs when bombarded with neutrons coming from a 241AmBe chemical source, autonomously obtaining the fundamental parameters that describe the formations
Relative density of the matrix
The Quad Neutron also has the following detectors: natural gamma ray, spectrum filtered gamma ray, CCL, fluid temperature (Top & Bottom), fluid resistivity (Top & Bottom) and an accelerometer. The communication method and the modular connectors used in the configuration of the tool allow other sensors to be included in the string for specific applications.
- Saturation and identification of fluids
- Volume of Clays
- Qualitative Permeability
- Relative Density of the matrix
- Identification o main lithologies (sandstone, limestone, dolomite)
- Identification of different types of fluids
When the rocks of the reservoirs and the fluids contained in them are bombarded with high-energy neutrons, three phenomenas occur:
- High-energy neutrons are slowed down mainly by collisions with the hydrogen element to thermal levels. The thermal neutron population counted by the N-N detectors is an inverse function of the concentration of hydrogen, also called the hydrogen index (HI).
- In this slowing down process, in each neutron collision, gamma rays of different energy levels are generated according to the element to which they have impacted. The population of gamma rays is inversely proportional to the density of the formation.
- When the thermal neutrons are captured, the activated atoms generate an additional set of gamma rays. The amount of gamma rays is a function of the type and concentration of the elements responsible for the capture (mainly, Cl-, Al +, Mg +). Gamma rays from activated Al + are the dominant in silicone formations and allows to evaluate the volume of clays. Also, in carbonate formations, activated Mg + is the dominant gamma ray generator and allows to evaluate the volume of Dolomite.
Being equipped with N-N and N-G sensors simultaneously allows extracting information -never previously used in the industry- from the neutron bombardment of a chemical source.
Principles of interpretation
The different measurements of the Quad Neutron and the sensitivity they have make it possible to obtain by empirical methods the different properties of interest of the formations. The identification of the fluids is based on the double superposition of:
Porosities QTP and QL, where QTP is the total porosity independent of the lithology and fluids and QL is the porosity affected by the different liquids. The sense of the separation and the magnitude of this allows us to identify and quantify the saturation of the fluid, since the separation is characterized by different porosities and fluids.
The superposition of QTP and DDN is a powerful assessment tool for the identification of light hydrocarbons and gas.
Since the methodology is relative (comparison) and the data is acquired by the same and only radioactive source, then it allows the evaluation to be carried out in a series of conditions that are not typically recommended for other technologies, such as, for example, drilling piping with the annular with fluid.
- Primary evaluation of the reservoir through tubing.
- By Passed zones with saturation of hydrocarbons.
- Monitoring of the reservoir over time.
- Evalution of new wells for any of the following reasons:
- Unattainable costs for open-hole loging in marginal fields.
- High risk wells for open-hole logging
- Saving of operating time in in-field drilling when doing the evaluation in cased hole: Saving in drilling rig, horizontal drilling, complex wells for open-hole logging.
- Water shut-off
- Water, Oil and Gas contacts evaluation
- Hydraulic fracturing monitoring with non-radioactive tracers.
- Heavy oil fields: With the ability to differentiate between the different types of fluids present in the field (heavy oil, light oil, gas, formation water)
- Wells completed with Gravel Pack / Slotted Liner systems or similar: without compromising the integrity of the obtained data. Unlike tools with pulsed neutron source (neutron generator, neutron accelerator, minitron), which lose precision in the presence of this type of completions.
- Horizontal wells with Coil Tubing (in memory mode); guaranteeing reaching maximum depths with minimum risk and maximum operational efficiency in areas of high demand.
Deployment options for the acquisition of the Quad Neutron Log
Wireline Logging: Real-time data acquisition
Coiled Tubing: Memory or real-time mode with e-Coil Tubing
Logging While Tripping: It logs comfortably when pumping the tool in memory mode inside the pipe until reaching a previously installed seat. It is logged when pulling out the drilling string at a given logging speed.
Slickline: Memory mode, “Smart Release” applications in memory, or in real-time with e-Slickline.
Drill Pipe or Tubing: In memory mode. The tool is placed in the pipe either when descending it or by pumping it later to log while moving the pipe.
Wells with Heavy Hydrocarbons 6 – 12 ° API, with the ability to differentiate between the different types of fluids present in the formation (heavy oil, light, gas and water formation).
Wells Completed with Sloted Liners / Gravel Pack systems, without compromising the integrity of the obtained data. Unlike tools with a pulsating source (neutron generators), which lose precision in the presence of this type of completions.
Horizontal Wells with Coiled Tubing (in memory mode); guaranteeing to reach maximum depths with minimum risk and maximum operational efficiency in areas of high demand.