Accurate reserve volume determination is crucial in the early stages of a project since planned subsurface capacity is dependent on reserve expectations. The fundamental method of calculating reserves uses bulk formation resistivity and bulk porosity to determine water saturation. This approach cannot accurately quantify reserves in laminated sand-shale sequences where the sensor resolution is insufficient to characterize the fine laminae. A tensor petrophysical model can determine laminar shale volume and laminar sand-fraction conductivities reducing the problem to a single dispersed shaly sand model. Combining this with sand-fraction porosities can lead to accurate reserve quantification.Identification and quantification of hydrocarbons within low-contrast, low-resistivity formations can be difficult when using conventional log data. This is primarily due to the presence of laminar shale and the inherent vertical resolution of measurements acquired by wireline and logging while drilling (LWD).A Gulf of Mexico deepwater example is used to demonstrate this novel approach in quantifying hydrocarbons in laminated sand-shale sequences. Real-time shear slowness is used in conjunction with LWD triple-combo data to identify potentially productive low-contrast reservoirs. Then, advanced resistivity post processing extracts the vertical component of resistivity, enabling calculation of sand-fraction resistivity. Sand-fraction resistivity, combined with normalized sand-fraction porosity, yields sand-fraction water saturation. Shale volume, porosity and water saturation cut-offs determine the net hydrocarbon volume. The LWD-calculated hydrocarbon volumes in place are then compared to results obtained from a wireline logging suite.This approach demonstrates that the use of conventional empirically derived bulk-volume porosity and saturation methods in laminated sand-shale sequence formations results in underestimation of the reservoir producibility and hydrocarbon reserves. Vertical resistivity, derived from LWD-acquired propagation resistivity and electrical anisotropy sensitivity, can be used to quantify reserves in these environments.

This paper presents some case histories involving multi-frequency quadrupole acoustic measurement to obtain the formation shear slowness under varying conditions. Quadrupole modes in high frequencies for fast formations acquired in parallel with low frequencies for slow formations are processed such that the final result is that the combination of both responses yield the shear slowness across the range encountered. These conditions range from large shallow boreholes with unconsolidated formations to consolidated formations where the shear velocity is faster or close to mud compressional velocity. As is well known in the industry, the monopole mode allows the measurement of shear slowness in fast formations. However, for slow formations this refracted shear does not exist which requires other means to be employed. The application of the dipole measurement which is used in wireline encounters problems in the Logging While Drilling (LWD) environment. These problems are due to the presence of the collar which greatly influences the flexural mode in the formation along with the additional signal caused by the collar flexural wave 1. Cases when the shear slowness lies in the range of the fluid slowness, a special treatment needs to be considered. The fact that one frequency (high or low) is unable to accurately respond above and below this threshold emphasizes the advantage and need for having multi-frequency LWD acoustic data to accomodate the demands of the environment. Also the challenging case where the shear slowness is in the same range as the mud compressional slowness will be discussed. All these results point to the importance of the use of a multi-frequency LWD acoustic tool for shear measurements. Some quality control considerations such as the rate of penetration (ROP) need to be taken into account in order to have a successful job. Introduction Accurate shear slowness data have become a fundamental measurement used by the oil industry in many areas: the shear slowness is used to identify the rock strength, shear failure, direction of stresses, and other geomechanical parameters involved in wellbore integrity; is also valuable in conjuction with the compressional slowness when pore pressure prediction models are built to avoid over pressure zones or borehole collapses. In seismic, the shear slowness allows estimating values of poisson 's ratios that are used to generate AVO (amplit ude versus offset) models for hydrocarbon identification or in ties with seismic when the compressional slowness response is not reliable, e.g. when gas zones are present on the seismic line. Because of these results, measuring the shear slowness only in fast formations is insufficient to create a complete borehole or reservoir analysis, especially when slow formations are present. Tang et al. 1 demonstrated that the LWD quadrupole tool is the best candidate for the shear measurement because the tool quadr upole wave is absent when operating in the low-frequency range and the quadrupole wave in a slow formation travels at formation shear velocity at low frequencies. In fast formations, the formation shear velocity can be measured from the second mode of the quadrupole wave. LWD acoustic data have been acquired in two wells from the North Sea and the Gulf of Mexico: The first example shows the acoustic processing over the North Sea data where the shear from the slow formation and the shear from the fast formation have been integrated to recreate a complete shear slowness response. The second example from the Gulf of Mexico, contrasts the shear slowness generated in fast formations from the high frequency quadrupole mode and the refracted shear processed from the high frequency monopole mode, showing the dispersive character of the refracted shear wave (result supported by modeling); also an example of the Acoustic Log Hydrocarbon Indicator (ALHI)7 and the hydrocarbon correction are presented.

Shallow drilling hazards present a significant risk to the health, safety, and environment of upstream oil and gas operations. Shallow marine formations are often near the critical porosity limit, where the sediment is very poorly sorted, mechanically weak and often unconsolidated. As the sediment begins to compact, well-construction challenges are created as formation stresses and fluid pressure changes, usually resulting in the operator having to set extra casing strings near the surface. The United States Department of the Interior, Minerals Management Service (MMS) requires the use of a diverter and a conductor string of casing if there is any possibility of a shallow hazard in the area of a proposed well. Proving shallow hazards do not exist in the area requires resistivity and porosity logs approved by the MMS. This operator requested these logs be run in 22 and 17 ½ in. boreholes using Logging While Drilling (LWD) technology as no wireline logging was planned. In large hole sizes, the porosity log is generally the limiting factor for most wireline and LWD technologies, with nuclear measurements from most vendors designed for hole sizes no bigger than 12 ¼ in. LWD Acoustic measurements in this well provided acceptable determination of porosity in borehole sizes up to 22 inches in extremely slow formations.The objective of this application was to acquire an LWD acoustic compressional slowness log below the drive pipe. Modeling shows and supports the ability to measure in this demanding environment where the compressional slowness often approaches that of the drilling mud. A 9 ½ in. LWD acoustic device was optimized for shallow data acquisition for the large borehole size and very slow acoustic velocities anticipated. While drilling, real-time LWD logs showed conclusive evidence of the absence of hazards and were immediately accepted by the MMS for the waiver. This paper validates the feasibility of using LWD logs to gain a conductor waiver from the MMS. Benefits include reduced operating costs associated with a wireline program and the savings involved in removing the conductor string from the casing program. On this multi-well batch drilling project operational savings of about 2.15 million USD were realized.

Shallow drilling hazards present a significant risk to the health, safety, and environment of upstream oil and gas operations. Shallow marine formations are often near the critical porosity limit, where the sediment is very poorly sorted, mechanically weak and often unconsolidated. As the sediment begins to compact, well-construction challenges are created as formation stresses and fluid pressure changes, usually resulting in the operator having to set extra casing strings near the surface. The United States Department of the Interior, Minerals Management Service (MMS) requires the use of a diverter and a conductor string of casing if there is any possibility of a shallow hazard in the area of a proposed well. Proving shallow hazards do not exist in the area requires resistivity and porosity logs approved by the MMS. This operator requested these logs be run in 22 and 17 ½ in. boreholes using Logging While Drilling (LWD) technology as no wireline logging was planned. In large hole sizes, the porosity log is generally the limiting factor for most wireline and LWD technologies, with nuclear measurements from most vendors designed for hole sizes no bigger than 12 ¼ in. LWD Acoustic measurements in this well provided acceptable determination of porosity in borehole sizes up to 22 inches in extremely slow formations.The objective of this application was to acquire an LWD acoustic compressional slowness log below the drive pipe. Modeling shows and supports the ability to measure in this demanding environment where the compressional slowness often approaches that of the drilling mud. A 9 ½ in. LWD acoustic device was optimized for shallow data acquisition for the large borehole size and very slow acoustic velocities anticipated. While drilling, real-time LWD logs showed conclusive evidence of the absence of hazards and were immediately accepted by the MMS for the waiver. This paper validates the feasibility of using LWD logs to gain a conductor waiver from the MMS. Benefits include reduced operating costs associated with a wireline program and the savings involved in removing the conductor string from the casing program. On this multi-well batch drilling project operational savings of about 2.15 million USD were realized.