Question

GAMMA RAY DEEP RESISTIVITY DENSITY P-WAVE VELOCITY 0 eapi 175 0 Oh 100 1.7 E/cc 2.7 1 ks 5 Layer A Layer B Layer C Layer D Layer E Layer G At the top of Layer F, we measured the following properties, Res 100 Ohm m, GR 40 api, Den 2.25g/cc, Vp 3.25 km/s. The reservoir including layers D, E and F is made by sand and shale. In the laboratory, we measured the following properties: the gamma ray of sand is 25 api, the gamma ray of shale is 175 api, the density of sand is 2.65g/cc, the density of shale is 2.1g/cc. The density of water is 1.00g/cc, and the density of the hydrocarbon is 0.7g/cc. Archie's exponents are n-2 and m = 2. The resistivitv of formation water is 0.1 Ohm m. 2.1. What can you tell about the lithology and the fluids in Layers A, B, C, D, E, F, and G. The interpretation is not unique. Provide the most likely interpretation for each layer and an explanation for each choice 2.2. From core measurements, we know that there is at least one layer made of calcite. Does 2.3. Explain what the purpose of fluid substitution in rock physics is (blue lines in Figure 1) 2.4.The interpretation is not unique. The company gives you a large additional budget to this information change the interpretation in 2.1? How? and how it can be performed acquire new logs in the well. What well logs would you acquire and how can they help to reduce the uncertainty in the interpretation?

Answer 1

2.1 Let's do it step by step. First, layer C is obvious indicating the presence of shale due to its high gamma-ray index. Layer D, E, F doesn't show much variation in their gamma-ray index, but they are showing high resistivity. This high resistivity is arising due to the presence of brine or may be hydrocarbons. Layer A is maybe the topsoil, while layer B is sand (see the change in P-Wave velocity). Layer G is maybe the carbonate rocks as P-Wave velocity is increasing.

2.2 If one layer is calcite, then the most possible one is layer G. Then it will serve as the source rock for the hydrocarbons present.

2.3 Fluid substitutions required to know the formation resistivity.

2.4 I would need SP Log for lithological details as well as sonic logs.