Geology (and other Earth Sciences)

the course im taking is (Petroleum Geology) 1 Announcing a Lease Sale Management requires your Evaluation by Monday 02/06 The following information has just been announced: ? The nation of Somewhereia has just announced an offshore lease sale in the Bonanza Basin. Eight blocks covering a total area of 2400 sq. kilometers will be offered. Bids are due 6 months from today. ? You have been asked to set up a team of up to 5 people to develop recommendations for senior management and, if appropriate, a bid strategy. The intent is to get you thinking about some of the issues people in industry face. Please provide a 2-4 pages report including: 1- Introduction 2- Discussions 3- Conclusions and Recommendations Assignments must be handed in at the specified time. Late assignments will receive an immediate 10% reduction in grade, with a 10% reduction in grade for each additional day the assignment is late. Provide a short list of the skills of you team and what are the issues each can best address. What are the main scientific/technical questions/issues? What are the main non-scientific/non-technical questions/issues? Geology 373 Exercise 1 Exercise 1: 10 points Geology 373 Exercise 1 2 You are asked to provide a quick ‘back-of-the-envelope’ evaluation of the blocks being offered offshore Somewhereia to determine if Is there enough potential that the company should take a serious look by investing significant exploration dollars. A check of in-house and public literature reveals that a well was drilled on the shelf, just updip from the open blocks. There is also a grid of 2D seismic lines. Both the seismic data and some information from the well are in the company records department. Figure 1 shows the location of the wells and available seismic lines. Figure 1. Index map showing the location of the A-1 well, the 2D seismic lines, and the open blocks. The well information is sparse, from a scouting service (Figure 2). However, there is good nearshore sandstone that would form a high-quality reservoir. A good marine shale lies above the sandstone. It should provide an adequate seal. Source rocks that should be able to yield oil are present in the well, but are immature (not buried deeply enough to start generating hydrocarbons). The conclusion from the well information is that there is a potential reservoir, source, and seal. The open blocks do hold promise if: (1) the source is more deeply buried, (2) the sandstone unit extends far enough out into the basin, and (3) the sandstones maintain good porosity further out into the basin, i.e., no facies change and not too much loss of porosity with greater burial depth. Geology 373 Exercise 1 3 Figure 2. Simplified stratigraphy for the A-1 well, based on information from scouts. A 2D seismic lines passes near the well location and has been interpreted to generate a cross-section. The potential source, reservoir, and seal units extend out to the open blocks, then they are cut away by a major erosional event in the early Tertiary. Although the units extend out into the basin, sedimentary facies may change downdip (e.g., the sandstone may grade into a siltstone or shale). The reservoir is also deeper and porosity decreases with depth. There are some rotated fault blocks. Geology 373 Exercise 1 4 Figure 3. A 2D seismic lines that passes near the A-1 well location and NNE out into the basin through block 2 and block 6. A study done at a university provides insights into how the Bonanza Basin formed. This study indicates that it is a divergent (pull-apart) margin with rifting during the Late Jurassic. The A-1 well is on normal continental crust, but most of the open acreage is on thinned continental or oceanic crust (Figure 4). This means higher heat flow and deeper burial for the open blocks than at the A-1 well location. This reduces the risk of an immature source rock. Geology 373 Exercise 1 5 Figure 4. A map showing the types and distribution of crustal types in the area of interest. Your team performs a quick interpretation using time to depth correlation of the top of the potential reservoir unit on the 2D seismic lines. Figure 5 shows your results (depths in kilometers). Over the open blocks, the potential reservoir varies in depth from about 500 m to 7000 m. Geology 373 Exercise 1 6 Figure 5. Top of the potential reservoir unit based on a quick interpretation of the 2D seismic lines and a simple time-to-depth relationship. NOTE: This map is adequate for a quick-look play analysis. If justified and approved by management more careful work would be required for prospect development. You have one more step to apply to this analysis. Using the well information, you model how the source rock would mature as a function of depth and how the reservoir porosity would decrease with depth. The results of this modeling are shown in Figure 6. Geology 373 Exercise 1 7 Figure 6. Modeling of source maturity (oil and gas generation) and reservoir porosity as a function of depth. You have a map to the top of the reservoir, but not one for the source. In the well the source is 400 m deeper than the reservoir, and on the seismic these intervals do not show much thickening or thinning. On Figure 7, indicate using color or shading where the reservoir is expected to be excellent, intermediate, and poor based on the model shown in Figure 6. Geology 373 Exercise 1 8 Figure 7. Map of reservoir quality (porosity) based on simple modeling. Indicate on this map your preliminary estimate of reservoir quality. From Figure 6, excellent reservoir quality is expected above a depth of 3500 m. Use color, shading, or a line pattern to indicate depths above 3500 m. Intermediate reservoir quality is expected between 3500 m and 4500 m. Use a different color, shading, or line pattern to indicate this depth range. Use a third color, shading, or line pattern to indicate where poor reservoir quality is expected. On Figure 8, show where you expect oil and gas generation to be occurring based on the model shown in Figure 6. (HINT: Subtract 400 m from the depths shown in Figure 6 to compensate for the 400 m depth difference between the reservoir and the source intervals.) Geology 373 Exercise 1 9 Figure 8. Map of source maturity (oil/gas generation) based on simple modeling. Indicate on this map your preliminary estimate of source maturity. This map is for the top of the reservoir, but we will use it by assuming the source is always 400 m deeper. Figure 6 indicates that above 3400 m the source is immature; it does not generate oil or gas. This area would be above 3000 m on this reservoir map (3400 – 400 m). Use color, shading, or a line pattern to indicate depths above 3000 m, where the source is immature. Similarly, indicate where (1) oil and (2) gas are being generated using different colors, shadings, or line patterns. In order to reach a go/no go decision and focus additional exploration, management wants to know which blocks if any promising? Justify your decision(s). Also are there any blocks that hold very little potential? Which ones? Justify your decision(s).