A 3D Seismic Survey Designing to Visualize the Oil Reservoir in West Kifl and Al-Marjan Fields, Central Iraq

Abstract


Introduction
Three-dimension seismic surveys (3-D) have become a major tool in the exploration and exploitation of hydrocarbons.Survey design depends on so many different input parameters and constraints that it has become entirely an art Laying out lines of sources and receivers must be done with an eye toward the expected results.A solid understanding of the required geophysical parameters must be in place prior to embarking a 3-D design project.Computer programs are now available to assist in this task (Kerekes, 1998;Al-Ameri and Al-Musawi, 2011;Handhal et al., 2020).
Geophysical parameters of 3-D survey can be gathered by imaging a wedge, geometrical and recording parameters.All of them have an impact on the 3-D data quality.They correspond mainly to the imaging parameters and are related to folding coverage, bin size and migration and signal enhancement and migration efficiency (Chaouch and Mari, 2006;Al-Musawi et al., 2020).In this research, 3-D seismic survey was designed for the West Kifl -Merjan oil fields which is one of the most important subsurface structures and one of the productive oil fields in Iraq as in Fig. 1 (Mohsain and Al-Khalidy, 2022).
Some previous surveys and studies are carried out o the study area.Limox (1972) studied an exploration survey where there was no closure in the area of interest.As well as, Mobile (1980) interpreted the seismic data of Coreg survey in 1980, giving a result for small closure (10m) in Hartha Formation with recommendation to drill an exploration well.O.E.C. (Oil Exploration Company -O.E.C, 1989. 1989. 2000, 2008, 2011) investigated deep formations of the Merjan -West Kifl field.
The main objective of this study is to use parameters of the 3D seismic survey in the fields of Marjan and West Al-Kifl using an active survey program to image the target reservoirs with high quality and resolution in order to help identify potential drilling sites and reservoir characterization studies.

Methodology
Collection of all the geological and geophysical information on the studied area, then statistically calculating the new 3-D geophysical parameters; Bin size, Maximum and Minimum offsets, Migration aperture, Inline and XL-line olds….Etc. to lay out the appropriate design parameters.Applying these parameters by modern computer software (MESA program, The Mesa project began as an open-source implementation of the OpenGL specification -a system for rendering interactive 3D graphics ) to get the result after applying the parameter in the field.Al-Khazraji et al., 2022 do three approaches of depth conversions: Models 1, 2, and 3 are applied from the simplest to the most complex on Nahr Umr Reservoir in Suba oilfield.This is to obtain the best approach, From the simplest to the most complex with the actual depth at well locations and good inter/extrapolation between or away from well controls.The results of these approaches, together with the uncertainty analysis provide a reliable velocity model and more accurate predicted depth that reduced the ambiguity of the subsurface.The uncertainty analysis reveals that Model 3 is considered a more practical and accurate approach because it gives a minimized standard deviation value of 14 with fewer residual and error values.
Analyzing the output data; Azimuthally and offset distribution, old at each depth, offset, rose diagram, and histogram before and after applying them in the field.Modeling and studying the subsurface reservoir that is based on this 3-D survey design.

Results and Discussion
The West Kifil-Merjan sparsely by wide-spaced 2D lines of different vintages from the 1980s.Seismic frequency information was extracted from this data at the target levels in order to decide on the survey parameters.
Depth structure maps interpreted by geophysical survey of Hartha, Zubair, above Najma and Karra Chine formations (Petrel Resources plc., 2007 andIdan et al., 2015).The survey area defined in this study was initially determined based on this map in 3D survey design.The results of the dip estimation are summarized in the Table 1.Exploration Target A target formation that has been adopted in good quality by the West Kifil-Merjan 3D survey design.It seems clear that the design covered a wide range from very shallow target Hartha 600m to below Kurra Chine 4000m and this design was made to resolve the stratigraphic complexity at the Hartha reservoir.The fold was increased to the very highest level (max.fold =380) to gain a high-resolution image at the shallow as well as the deep target.From the Me-1 and Wk-1 wells, depth-interval model was derived.Velocity-depth interval curves, and other velocity functions were calculated (Fig. 2).They were used in the following sections to estimate bin size, migration distances, mute function, maximum useable, and fold maps as a function of time.

Acquisition Parameters Design and Proposal
Key acquisition parameters, such as bin size, offset and folds, etc., were considered in the geometry design based on the existing 2D data and geological objectives.Based on the data of Me-1 and Wk-1 wells, structures map and velocity information, they were important to image sallow horizon clearly for both conversion and resolve the reservoir ambiguity or uncertainty at Hartha stratigraphic traps and to the development history restoration.The geophysical model parameters, which are listed in Table 2, it is selected for the survey area.

Resolution Requirement
The velocity information was used to analyze different scenarios where the input geological data was useful: • Reservoir thickness observed in wells.
• Minimum reservoir depth for current reservoir.Several expressions and criteria for the computation of vertical and lateral resolution have been published in the literature.Two of the simplest of these expressions are Vertical resolution: Vint / N*Fdom ≤ Rv ≤ Vint / Vint / N*Fdom Bin ≤ Lateral resolution ≤ Vint / 4*Fmax*sinӨ With 2 ≤ N ≤ 4 assumed that lateral resolution was between one quarter and one-half the dominant wavelength.
A bin size less than one-quarter of the dominant wavelength results in over-sampling and provides no additional information.The use o a bin size greater than half o the dominant wavelength will result in spatial aliasing and missing information.
Ө is the maximum aperture usually 30 degrees for initial evaluations.Using these expressions and the target information o Table 3, the following estimations for the resolution requirement can be computed.The selection of the bin of the survey needs to be sufficient to adequately sample the target information without poor sampling of the survey targets and without overspending on the acquisition of the survey (Japan Consortium, 2008 andAl-Khazraji et al., 2022).Using the available depth and velocity information, the theoretical diffraction curves for the intended target can be constructed.

Bin Size Calculation
1) Target size Target size / three Sturge's rule is another way to choose bin sizes.Although it's widely used in statistical packages for making histograms, it has been criticized for over-smoothing histograms (Hyndman and Athanasopoulos, 2013).Therefore it should probably be considered a "Rule of Thumb" rather than an absolute formula with the perfect solution.Three traces across a small target, 9 traces on a time slice horizon.Most statistical packages use Sturges' rule (or an extension of it) for selecting the number of classes when constructing a histogram.Sturges' rule is also widely recommended in introductory statistics textbooks.It is known that Sturges' rule leads to over-smoothed histograms, but Sturges' derivation of his rule has never been questioned.On this note, I point out that the argument leading to Sturges' rule is wrong.Therefore it should probably be considered a "Rule of Thumb" rather than an absolute formula with the perfect solution (Hyndman and Athanasopoulos 2013) From the above, when looking at the actual dip, a bin size of 25m was adequate for frequencies up to 100Hz.Also taking into account direction tails and adults, and therefore looking at dips 0 up to 30 degrees.A bin size of 25 m can then handle frequencies 0 up to 62Hz.Existing seismic data displayed earlier, and data room nearby areas, showed that frequencies 0 up to 55-60Hz may be recoverable.This led to the recommendation to use a 25×25m subsurface bin size, corresponding to 50m source and receiver intervals on the surface.

Selection of Maximum-Minimum Offset
The range of target depths from 488m to 4200m imposed an important constraint on the offset range that needed to be used.For the survey design, the maximum offset was in first instance determined by the largest offset that contributed to imaging the deepest horizon of interest, taking into account the subsurface dips and velocities.Xmax -Xmin should be equal to the target depth approximately.The maximum offset for this project was 4200 m and the minimum offset was about 200 m (Fig. 3).This Xmax -Xmin was calculated by following equations Xmin = (RLI 2 +SLI 2 ) 1/2 Xmax = (Xcross 2 +Xin 2 ) 1/2 Where X min: maximum offset RLI: Receiver Line interval

Fold
For an orthogonal design with 200*200 m line spacing, inline offsets of 3376 m and cross line offsets 1977 m, fold maps were generated at 4 key horizons, using the depths in well Me-1 and Wk-1, and the maximum offsets at these depths derived earlier (Table 5).The subsurface bin cell size was 25*25 m.Fig. 5 shows the effective fold of full area of West Kifl-Merjan oil fields.
Table 5 summarizes a number of possible seismic acquisition geometries for each of these surface conditions, expressed in surface line number km² per km², and estimated relative costs.It is clear from the table that Folds is the largest at the third option, equal to 380, which is the largest when compared to the first and second options. Merjan

Fig. 1 .
Fig. 1.Location map of the study area

Table 1 .
Estimated maximum structural dips of key horizon/depth

Table 2 .
Summary of the geophysical parameters for the intended targets

Table 3 .
Shows lateral and vertical resolution in West Kifl-Marjan field

Table 5 .
Shows three Geometry Proposal Fig. 4. Survey theoretical boundaries