After discovering oil in a field, several studies are necessary to understand the reservoir's heterogeneity, determine its three-dimensional extent, evaluate fluid volumes, and find the best method to enhance fluid recovery. The reservoir's performance and development plans depend on factors like lithofacies heterogeneities, porosity, and permeability spatial variation. [1].
A 3D model is a mathematical representation of a three-dimensional object or surface created using specialized software. It's also known as a 3D model. Generally, a model represents an object or event in the real world, and it's considered good if it accurately describes relevant properties for a specific study. For instance, a 3D geological model is considered good if it accurately reflects real-world values for reservoir simulations and modeling. Different models may be used for various purposes to achieve the best results. A geological model specifically represents the spatial distribution of sediments and rocks beneath the surface. [2].
The production capacity of a reservoir relies on its geometric, structural, and Petrophysical features. Creating a reservoir model is crucial for predicting reservoir behavior as it integrates various information within the structural framework and stratigraphic layers. The 3D geological model also shows the distribution of properties like porosity, permeability, and water saturation between wells. [3].This method allows the reservoir modeler to estimate reservoir properties between wells using observed data points and statistical prediction. [4]. In the current study, fourteen wells from X oilfield (Well-1, Well-2, Well-3, Well-5, Well-6, Well-9, Well-10, Well-11, Well-12, Well-13, Well-14, Well-15, Well-25, Well-34 and Well-35) have been selected to study Y- Formation (Lower Cretaceous).
The goal of this research is to create a 3D integrated model using Petrel software, which enables 3D visualization, mapping, and reservoir modeling and simulation. This model incorporates the structure, Facies, and distribution of Petrophysical properties (porosity, water saturation) in three dimensions. [5].
Volumetric estimation, often referred to as the "geologist's method," relies on cores, wireline log analysis, and geological maps. A reservoir rock is characterized by porosity and permeability that hold a significant amount of extractable hydrocarbon, while also containing hydrocarbons. In contrast, a non-reservoir rock typically has low porosity, low permeability, and low or zero hydrocarbon saturation. The primary controlling factor is the basic lithology; for instance, shales may contain hydrocarbons but have high water saturations and low permeability, making them non-reservoir rocks. [6].
The volumetric method is a simple approach that involves determining the reservoir's area, pay thickness, rock pore volume, and fluid content within the pores to calculate the amount of hydrocarbons in place. The ultimate recovery can then be estimated using a recovery factor. However, each of these variables has its own uncertainties, which, when combined, can lead to significant uncertainties in the reserves estimate. [7].
Geological Background
Carbonate sequences represent an important global hydrocarbon resource. Y- Formation deposit at the lower cretaceous, and its stratigraphic position between Khasib formation from the top and Rumaila formation from the bottom. The lithology of Y-Formation at this oilfield is Limestone and dolomite, with interbedded layers of shale. Besides that, the Y- Formation is divided to three units (MA, MB and MC). Figures (1) shows the stratigraphic column of Y- Formation with age and lithology descriptions. Fourteen wells was drilled in X oilfield as shown as in figure (2). The Y- Formation shows considerable variations in lithology, porosity, and permeability that add to the reservoir's heterogeneity and affect the flow of oil and gas within the field. The Y- Formation is best developed as thick rudist buildups over structural highs in southern region, specifically in the eastern Mesopotamian Zone. [8].
Oil occurrences in Y- Formation reservoir have been identified in 32 structures spanning northern, central, and southern. The most substantial net reservoir thickness is observed within the rudist banks of East Mesopotamia. Porosity ranges up to 22%, with an average of 15%. Permeability shows good variability, ranging from 23 to 775 millidarcies (md).
The API gravity of the oil found in Y- Formation typically falls within the range of 23 to 36.6 degrees, with an average of approximately 25 degrees, [9]. Y- Formation is considered equivalent to the top part of the Massad Formation in the Rutba area, [10], as well as the Jerebi and Merka formations in western Iraq, [11]. It also corresponds to various formations in neighboring countries, including the Maqwaa Formation in Kuwait, the Natih Formation member € in Oman, the Al-Khatea and Rumaila Formations in the northern UAE, and the Salabikh Formation member Schiliaf in Abu Dhabi. Moreover, in Saudi Arabia, it is located within the Wasia group, and in Iran, it is equivalent to the top part of the Sarvak Formation, [12]. Y- Formation shares the same naming in both Qatar and Bahrain.
Objectives of Study
The main purpose of the present study is building 3D-geological model includes structural, Facies and Petrophysical models using Petrel software and evaluating the oil-in-place for Y- Formation, which is consider an important in estimating oil reserves and play a major role in the economics of oil.
Model Workflow
The research utilized data from X oilfield in southern region, specifically for Y- Formation. This data included contour maps and well logs. After proper organization, the data was imported into Petrel software to construct the 3D reservoir model. The workflow design for the study involved a variety of functional tools available in Petrel, such as 3D visualization, well correlation, 3D mapping, and 3D grid design for geology simulation, well log upscaling, Petrophysical modeling, data analysis, and volume calculation. Figure 3 provides a visual representation of Y- Formation workflow model.