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This paper describes the workflow to derive a robust depth reference case map and associated depth uncertainty range suitable for use in the planning of new wells and for ‘gas in place’ calculations. DGI's Covizsoftware was used to deliver this objective. A number ofseismic and well velocity inputs and seven methodologies were tested withPre-stack depth migrated (PSDM) interval velocities chosen as the most reliable for geologic top prognoses (based on drop-out test results). All other methods were used to frame the uncertainties around this reference case. This methodology was tested in the recent ABCXX8 well with a resultant depth prediction error at the reservoir level of 0.5%. However, it should be noted that distance from nearest control point is a crucial factor in the prediction of depth and corresponding depth uncertainty. Further updates of the calibration model will be made with an upcoming regional well trade and the latest wells on the block. Covizallows rapid updating of the model with any new information.

The degree of fluid compartmentalization has direct implications on the development costs of oil and gas reservoirs, since it may negatively impact gas water contacts (GWC) and fluid condensate gas ratios (CGR). In this case study on the Barik Formation in the giant Khazzan gas field in Block 61 in Oman we demonstrate how integrating independent approaches for assessing potential reservoir compartmentalization can be used to assess compartmentalization risk. The three disciplines that were integrated are structural geology (fault seal analysis, movement and stress stages of faults and fractures, traps geometry over geological time), petroleum systems (fluid chemistry and pressure, charge history) and sedimentology-stratigraphy including diagenesis (sedimentological and diagenetic controls on vertical and lateral facies and reservoir quality variation). Dynamic data from production tests were also analyzed and integrated with the observations above. Based on this work, Combined Common Risk Segment (CCRS) maps with a most likely and alternative scenarios for reservoir compartmentalization were constructed. While pressure data carry significant uncertainty due to the tight nature of the deeply buried rocks, it is clear pressures in gas-bearing sections fall onto a single pressure gradient across Block 61, while water pressures indicate variable GWCs. Overall, the GWCs appear to shallow across the field towards the NW, while water pressure appears to increase in that direction. The "apparent" gas communication with separate aquifers is difficult to explain conventionally. A range of scenarios for fluid distribution and reservoir connectivity are discussed. Fault seal compartmentalization and different trap spill points were found to be the most likely mechanism explaining fluid distribution and likely reservoir compartmentalization. Perched water may be another factor explaining variable GWCs. Hydrodynamic tilting due to the flow of formation water was deemed an unlikely scenario, and the risk of reservoir compartmentalization due to sedimentological and diagenetic flow barriers was deemed to be low.

The reproductive biology and feeding habits of the Indian oil sardine Sardinella longiceps Val. studied from the coast of Mahout, Oman for a period of 2 years from September 2007 to September 2009 are described. The presence of mature and spent gonads from July to September and in January to February during 2007–2008 and June to September and January in 2008–2009 indicated two peaks of spawning periods in the population of S. longiceps; however, the periodicity differed slightly between the years. Higher monthly gonadosomatic indices (GSI) and relative condition factor (Kn) corroborated with the spawning season. Males and females matured (50%) at an average length of 187 and 191 mm, respectively. The annual sex ratios (male to female) were 1:1.56 during 2007–2008 and 1:1.66 during 2008–2009. Fecundity of individual fish ranged from 35,568 eggs to 96,259 eggs with an average of 71,835 eggs. The fish fed primarily on diatoms, while dinoflagellates, copepods and fish eggs were of minor importance.

The concept of Specific Drilling Energy (SDE) has been in existence for decades and used in both the mining and oil industries to mainly optimize drilling performance and efficiency. We present a practical application of SDE to pick key lithological boundaries during and post drilling. This in turn is serving as an additional tool used to aid well operations and also characterise the overburden of the Khazzan Field. Developing the giant Khazzan Gas Field requires drilling a large number of wells to the deep target reservoir. Characterizing the overburden in such a field requires a consistent approach in defining the overburden geological formations to aid drilling operations, selecting casing setting points andavoiding future drilling surprises in planned wells. The concept of specific drilling energy is being applied in the Khazzan Field to aid Geologists in three ways:Firstly, picking shallow formation tops for top holes drilled by a rig with no mud logging unit. Secondly, real time picking of shallow formation tops besides potentially removing cuttings lag time factor and consequently to ensure correct casing setting depths in order to avoid wellbore stability issues. Thirdly, it serves as an additional tool to QC formation tops post drilling particularly for tops picked in the absence of petrophysical logs. Various forms of the equation have been developed through time to mainly assist drillers optimize drilling performance. In this case, thevery earliest form proposed by Teale in 1965 was used in which main inputs into the SDE equation include Rate of Penetration (ROP), torque, Weight on Bit (WOB) and Rotations per Minute (RPM) which are readily recorded by drilling sensors at no extra cost. When this data is loaded into petro-technical software, such as Petrel in this case, the powerful display functionality allows comprehensive correlation between wells and eases the process of picking formation tops. A few examples are presented upon which this methodology aided picking the top of a casing setting formation, calling total drilling depths and performing correlations between wells post drilling to aid the provision of tops prognosis in future planned wells. This work proves that the applications of the SDE concept is not just limited to drilling optimization, but also in assisting Geoscientists identify lithological boundaries and aid informed decisions in well operations using solely drilling parameters.

Morphological characteristics of Indian oil sardineSardinella longicepsof sagittal otolith were investigated in the Sea of Oman at Muscat area during the period of one year from October 2008 to September 2009. A total of 152 otolith specimens were used for otolith morphometric analysis purposes. The sagittal otolith measurements including length, width and weight of otolith were obtained to assess whether there were differences between left and right otoliths of the fish and to examine otolith-fish size relationships of the species. The value of coefficient of determination R2of 0.9 showed strong correlation between right and left otolith measurements (length, width and weight), suggesting there was no significance variation in otolith for both sides and this may influence the growth rate of the species. Otolith morphometric observation including length, width and weight were correlated with total length of the fish representing R2ranged from 0.902 to 0.986 indicating that dimensions of otolith in the species grow in proportion to the total length and weight of fish.

The study of seismic anisotropy in exploration seismology is gaining interest as it provides valuable information about reservoir properties and stress directions. In this study we estimate anisotropy in a petroleum field in Oman using observations of shear‐wave splitting from microseismic data. The data set was recorded by arrays of borehole geophones deployed in five wells. We analyse nearly 3400 microearthquakes, yielding around 8500 shear‐wave splitting measurements. Stringent quality control reduces the number of reliable measurements to 325. Shear‐wave splitting modelling in a range of rock models is then used to guide the interpretation. The difference between the fast and slow shear‐wave velocities along the raypath in the field ranges between 0–10% and it is controlled both by lithology and proximity to the NE‐SW trending graben fault system that cuts the field formations. The anisotropy is interpreted in terms of aligned fractures or cracks superimposed on an intrinsic vertical transversely isotropic (VTI) rock fabric. The highest magnitudes of anisotropy are within the highly fractured uppermost unit of the Natih carbonate reservoir. Anisotropy decreases with depth, with the lowest magnitudes found in the deep part of the Natih carbonate formation. Moderate amounts of anisotropy are found in the shale cap rock. Anisotropy also varies laterally with the highest anisotropy occurring either side of the south‐eastern graben fault. The predominant fracture strikes, inferred from the fast shear‐wave polarizations, are consistent with the trends of the main faults (NE‐SW and NW‐SE). The majority of observations indicate subvertical fracture dip (>70°). Cumulatively, these observations show how studies of shear‐wave splitting using microseismic data can be used to characterize fractures, important information for the exploitation of many reservoirs.

The use of multicomponent receivers allows one to record the complete elastic wavefield. This is desirable since knowledge of both P- and S-wave characteristics yields better insights into subsurface lithologic and structural rock properties than P-wave knowledge alone. It is often assumed in multicomponent processing that the vertical z-component contains principally pure-mode P-wave arrivals and that the inline horizontal x-component consists mainly of P-SV convertedwave energy. This assumption actually becomes worse with increasing offset. Contaminating energy on either component should ideally be removed to prevent degeneration of stack quality. Often, the x-component is more contaminated than the z-component because P-wave incidence angles (from vertical) are larger than those of P-S waves. This renders processing of the x-component more challenging. Removal of contaminating energy on either component may lead to sharper images. One way of removing such undesired energy is by means of wavefield separation. We propose a simple, approximate wavefield-separation scheme in the τ -p domain to better

Capture of a great Longtail tuna, Thunnus tonggol from off Shore of the city of Salalah, Arabian Sea, Sultanate of Oman in January 2013 is described in this paper. Its morphometric and meristic characters are discussed.

This paper details the successful downhole microseismic monitoring of a number of hydraulic fracture treatments in a horizontal well drilled in the Barik reservoir, integrating the results with treatment data. The treatment well was drilled in a direction of 312°, at 90° to the assumed maximum stress direction, with a horizontal section of 1000m. The well was placed such that it passed within 300m of the well to be used as the observation well. The observation well was plugged immediately above the topmost reservoir perforations to minimize disturbance in micro-seismic data. The maximum geophone array length from the top of the plug to the production string was therefore 60m. A number of fracture treatments were monitored, with the results giving understanding of fracture placement, direction, length, and height. The early results impacted immediate decision making on perforation strategy. Orientation of the maximum principal horizontal stress was confirmed. Overall frac height appears to demonstrate effective coverage of the Barik reservoir interval. This key data will strongly influence future completion design and the overall development plan of the field.

A tight gas case history from the North America Rocky Mountains shows the capability of borehole microseismic and 3D seismic anisotropy to delineate fracture systems induced in a clastic reservoir by hydraulic fracturing of a horizontal well. Dual monitoring of the horizontal well completion indicates improvements in fracture mapping by compressing hypocenters of the microseisms to more linear features that are corroborated by production logging flowmeter. Fracture half-lengths and vertical heights of fractures are indicated for reservoir modelling. Advanced processing of the microseismic 3-component geophone first motions indicates fracture azimuth and dips from a moment tensor inversion and suggests a conjugate set of orthogonal fractures in the reservoir. 3D seismic anisotropy results, using a fast and slow velocity direction calculated from the data, suggest inherent microfractures present in the rock prior to completion. Surface fault mapping in the field supports fractures mapped by both the microseismic and the 3D seismic anisotropy. Multiple regression analysis of drilling, completion and 3D seismic anisotropy parameters versus initial production for 30, 90 and 180 days results show independent contributions to production. A predictive production model based on the multiple regression analysis allows for future well planning and completions to optimise well performance.

Fracture size is one of the main parameters that reservoir engineers are interested in due to its importance in hydrocarbon production. We estimate the fracture size using the Chapman (2003) theory of frequency-dependent shear-wave splitting on microseismic data recorded in the Yibal field. The Natih A reservoir demonstrates the largest fracture size and fracture density of 2 m and 0.07-0.23, respectively, as expected for a highly fracture reservoir. In contrast, the Fiqa exhibits moderate fracture density (3%) with fine-scale fractures (

Fault plane solutions (FPSs) are estimated for microseismic events in the Yibal field, west-central Oman. We analyse 22 days of data, containing over 600 located events recorded by a maximum of 5 monitoring wells (10 downhole 3-component stations in total). 43 reliable FPSs are determined using polarities and amplitudes of direct P-, SV- and SH-waves and based on assumption of a pure double-couple source. The analysis was guided by tests with synthetic data, which were generated by the reflectivity method. We observe a transition in faulting regime from strike-slip (with a thrusting component) in the shale Fiqa cap rock to pure thrusting in the gas-charged Natih A chalk reservoir. Deeper in the field we observe another transition from strike-slip in the Nahr Umr shale cap rock to normal faulting in the oil-bearing Shuaiba chalk reservoir. Collectively the results suggest that the fault regime is controlled by style of deformation and lithology.

P094 P000 MICROSEISMIC MONITORING AND SPATIAL VARIATIONS IN ANISOTROPY AN EXAMPLE FROM OMAN. A. AL-ANBOORI 1 M. KENDALL 1 D. RAYMER 2 and R. JONES 2 1 School of Earth and Environment University of Leeds Leeds LS2 9JT UK. 2 Vetco Gray Ltd Rosemanowes Penryn TR10 9DU UK. Summary Measurements of shear-wave splitting in microseismic data are used to study seismic anisotropy in an oilfield in west-central Oman. Over 460 events are recorded by up to 10 downhole seismometers deployed in 5 boreholes resulting in nearly 2500 shear-wave splitting measurements. Stringent quality control reduces the number of reliable measurements to

We summarize observations of shear-wave splitting from passive seismic monitoring in a range of petroleum settings. Such measurements are relatively rare, but the emerging picture is one of fracture-induced anisotropy where a number of factors control both spatial and temporal variations. These observations offer insights into the state of stress in a reservoir and can serve as a ground-truth for geomechanical models.