Oil and natural gas are not only our main energy source, but are feedstocks for synthetic materials, pharmaceuticals and various other petrochemical and chemical products. Global proven oil and gas reserves have continuously increased since 1980s, with 2016 seeing an increase of 0.9% due to continuous developments and improving technologies that have enhanced exploration and recovery techniques. Reservoir modelling using 3D-modelling systems is an effective technique in reservoir management that allows for the integration of seismic and well log data to produce models that can be used for various purposes such as reserve estimations, commerciality decisions and re-development of old fields. Despite exploitation of renewable energy sources, fossil fuels remain the most convenient sources of energy, with the demand for oil and gas driving the development in technology in order to assess the certainty of, and reduce the risk of hydrocarbons. If the advance of technology continues, current resources that are not yet economical to extract may become economical in the future.
The Longhorsley-1 well (well number: L34/22-1) is located in Northumberland, England (Lat: 55o 13' 36 80"N. Long: 01o 46' 22 60"W) and was first explored in 1986 by Candecca Resources PLC with the objective of investigating its lithologies. The well was drilled to a total depth of 6000 feet and has since been plugged and abandoned.
Aim
The main aim of the project is to integrate petrophysical data with seismic data to produce a 3D model in order to gain a high resolution subsurface image of the previously exploited Longhorsley-1 well. The outcome of this project will allow for an evaluation of the potential of the well to be revisited as well as an opportunity to assess the advantages and disadvantages of new 3D-modelling systems and their scope for future use.
Objectives and hypotheses
Petrophysical analysis requires information to be obtained from the well log of Longhorsley-1 including its lithological data in addition to porosity and permeability values, measured from samples taken where its rock types are exposed on the coastal section. Original 3D seismic data has to be sourced, consisting of several lines that pass through the location of the Longhorsley-1 well in the format required for the modelling software – GeoTeric. The final model produced with the GeoTeric software can then be used to illustrate the effectiveness of 3D-modelling in the exploration for hydrocarbons and to assess the need for further recovery from the well.
Scope
The project will involve correlating the beds within the borehole to the coastal outcrop section. Samples of each bed will be taken and subject to permeability and porosity tests. Porosity measurements will show the capacity of oil the rock can contain whilst permeability measurements will show the capacity of the rock to transport fluids. For a more in-depth study, thin-sections could have been produced in order to assess the quality of the reservoir based on pore-scale properties such as grain density by using electron microscopes. However, this would have been time consuming and costly. Another petrophysical quality that accompanies porosity and permeability is to work out water saturation to identify potential areas saturated with water. However, this is not as important as porosity and permeability1 therefore will not be investigated.
Initial Literature Review
A recent study undertaken by Godwill and Waburoko (2016) used 3D reservoir modelling on the Zilaitun oil field, China, to provide an accurate description and visualisation of reservoir heterogeneity. Their study used petrophysical data including porosity and permeability values to develop the potential of remaining oil in the reservoir as well as 3D seismic data and well data to construct a 3D reservoir model. The study showed the versatility of integrating well log and seismic data for reservoir modelling and found that the reservoir properties in the field are controlled by two main faulting regimes. The data gathered and construction of the model has provided evidence that the Zilaitun oil field should be further exploited for its economic importance. This study aims to produce a 3D model that can provide similar results: evidence for the potential of revisiting a previously exploited reservoir and to demonstrate the effectiveness and highlight any weaknesses of 3D-modelling.
The mercury injection capillary pressure (MICP) porosimetry technique for analysing petrophysical properties will be used in the project as it is the most common method in industry of characterising pore-throats and volume-weighted pore size distribution of porous solids. MICP is effective for macroporous samples therefore is likely to be the best method for this project as the lithology associated with the Longhorsley-1 well is mainly sandstone.
Proposed Methodology
♣ Seismic Data Acquisition: The seismic data needed in this project is not readily available therefore requires permission from seismic data release agents. Four seismic lines have been found using the UK Onshore Geophysical Library (UKOGL) that intersect the Longhorsley-1 well. UKOGL will be contacted in order to obtain the original seismic data in the correct format for use with the GeoTeric software.
♣ Sampling Coastal Section: Prior to using the seismic data, physical data needs to be acquired. Longhorsley-1 is approximately 35km from the North-East coast of England. Using the well log data that displays the lithology of the well, the beds within the well will be correlated with the outcropping beds on the coastal section and samples large enough for analysis will be taken. Before samples are taken, the British Geological Survey (BGS) Lexicon of Named Rock Units will be used to identify individual bed properties of each unit within the well – meaning some beds may be grouped together for sampling and analysis as their differences in lithology may be very minor for porosity and permeability measurements.
♣ Permeability and Porosity Measurement: The MICP porosimetry technique will be used to determine the permeability and porosity of each sample using a Micromeritics Autopore II 9220 Mercury Injection Porosimeter, located on the Newcastle University campus. Mercury is injected through the sample, increasing the imposed pressure in small increments and then the volume of mercury that enters the sample during each pressure increment is measured.6 Porosity and permeability can then be calculated from pore-throat values using the Washburn equation: p = -2cosr
where: p = imposed pressure = surface tension = contact angle r = radius of pore CHECK WITH DAVE + SAMPLE SIZE
♣ GeoTeric 3D-modelling: Petrophysical data will then be integrated with the correctly formatted seismic data (SEG-Y) and input into the latest GeoTeric software: GeoTeric 2017.2.1 to produce a model of the Longhorsley-1 well.
Skills Requirements
Accurate identification of different rock layers is required at the coastal section in order to successfully correlate the beds to the borehole. It is important to know how to correctly identify certain rocks based on features described using the BGS Lexicon of Named Rock Units. In addition, although help will be provided using the mercury injection porosimeter, training will be needed to be able to interpret the data that is produced from each sample and any further calculations required. GeoTeric will provide training for the use of their software at their Newcastle headquarters. MORE????
Resource Requirements
Seismic data must be collected from UKOGL for:
♣ Seismic data in the SEG-Y format, of lines:
1. THEL-87-02
2. C85-116
3. C85-117
4. CAN-84-112
Well data release agent, CGG, must be contacted for provision of the Longhorsley-1 well data. This well log data is required in the ASCII/Petrel format for use in GeoTeric. In addition to input data, access to a computer with the pre-requisites required for the use of the software includes:
♣ At least Windows 7 operating system or Red Hat Linux Enterprise (RHEL) 6
♣ Installation of an NVIDIA driver
♣ Three packages: X Window System, GNOME Desktop Environment and Open Motif
Requirements and equipment for sample retrieval:
♣ Transportation to and from the coastal section
♣ BGS Lexicon of Named Rock Units for information on the rock types within the Longhorsley-1 well
♣ Geological hammer
♣ Safety goggles
♣ Hard hat and hi-visibility vest
♣ Sturdy footwear
♣ Sample bags
♣ Hand lens
♣ Measuring apparatus
♣ Samples of each bed
Requirements for permeability and porosity measurements:
♣ Access to laboratory, room 4.16 in the Drummond Building, Newcastle University for the use of the Micromeritics Autopore II 9220 Mercury Injection Porosimeter
♣ Supervision of use of porosimeter
Programme of Work
Anticipated Outcomes
By the end of the project, a high resolution, 3D model of the Longhorsley-1 well will be produced from integration of seismic and petrophysical data, that can be studied for recognition of subsurface geology as well as the presence of faulting within the well’s lithology. The model produced provides a subsurface image that geoscientists can interpret with higher confidence compared to previous techniques. This method of displaying the features of the well can be critically reviewed to state both positive aspects and possible drawbacks for the use of 3D modelling in future studies. In addition, the provision of a 3D model of the Longhorsley-1 well could be used to determine whether it would be feasible to revisit the well for further resources.