Influence of reservoir damage, reservoir length and thickness on the inflow characteristics of horizontal wells



Optimizing the productivity of horizontal wells requires a thorough understanding of reservoir properties, careful selection of completion techniques, effective stimulation treatments, and the implementation of appropriate production strategies. The following is a summary of the key findings from some relevant studies.

Keywords: optimizing, productivity of horizontal wells, reservoir damage, reservoir length, reservoir thickness.

Introduction. The literature on the influence of reservoir damage, reservoir length, and thickness on the inflow characteristics of horizontal wells provides valuable insights into the factors that affect the production performance of such wells.

Reservoir damage. Reservoir damage refers to the reduction in permeability caused by various factors, such as drilling fluids, fines migration, and scale deposition. Studies have shown that reservoir damage can significantly affect the inflow performance of horizontal wells. For instance, [2] found that the presence of a high-permeability zone (HPZ) adjacent to the wellbore can reduce the impact of damage on the inflow performance of horizontal wells.

Reservoir length. Reservoir length is a crucial factor that affects the inflow performance of horizontal wells. Longer reservoirs generally lead to higher productivity, as they provide more contact area between the wellbore and the reservoir. However, there is a limit to the length of the reservoir that can be effectively drained by a horizontal well. Several studies have shown that the productivity index (PI) of horizontal wells decreases as the reservoir length increases beyond a certain threshold [1].

Reservoir thickness. Reservoir thickness is another critical factor that affects the inflow performance of horizontal wells. Thicker reservoirs generally lead to higher productivity, as they provide more volume of oil and gas to be produced. However, the effectiveness of a horizontal well in draining a thick reservoir depends on several factors, such as the wellbore trajectory, completion design, and reservoir properties. Studies have shown that the PI of horizontal wells generally increases with increasing reservoir thickness, up to a certain limit, beyond which the PI reaches a plateau or even starts to decline [1].

Overall, the literature suggests that the inflow performance of horizontal wells is affected by a range of factors, including reservoir damage, length, and thickness [3, 4].

Methods. The key to maximizing the productivity of horizontal wells is to optimize these factors through careful well planning and design, based on a thorough understanding of the reservoir properties and characteristics.

Selecting the right completion technique for a horizontal well depends on several factors, including reservoir properties, formation type, and the desired production goals. Here are some of the commonly used completion techniques for horizontal wells:

1. Open-hole completion: This technique involves drilling and completing the well without any casing or liners. Open-hole completions are often used in high-permeability reservoirs where sand production is not a concern.
2. Cased-hole completion: In this technique, the wellbore is cased and cemented, and perforations are made in the casing to allow oil and gas to flow into the wellbore. Cased-hole completions are commonly used in low-permeability reservoirs and where sand control is necessary.
3. Slotted liner completion: This technique involves the use of a slotted liner, which is inserted into the wellbore and cemented in place. The slotted liner allows oil and gas to flow through the slots while preventing sand production.
4. Gravel-packed completion: This technique involves the use of a gravel pack to prevent sand production while allowing oil and gas to flow into the wellbore. Gravel packs are commonly used in unconsolidated formations.
5. Hydraulic fracturing: This technique involves injecting a fluid at high pressure into the formation to create fractures and increase the permeability of the reservoir. Hydraulic fracturing is commonly used in low-permeability reservoirs to enhance well productivity.

The choice of completion technique depends on the formation properties, reservoir characteristics, and production goals. It is important to consider the impact of each completion technique on the productivity and the long-term performance of the horizontal well.

The region of a reservoir with the highest oil and gas saturation is commonly referred to as the «sweet spot». The sweet spot is the area where the concentration of hydrocarbons is highest and where a horizontal well can be most productive.

To locate the sweet spot, geologists and reservoir engineers use various techniques such as seismic surveys, well logs, and core samples. By analyzing the geological properties of the reservoir, they can identify the most promising areas for horizontal well placement.

Once the sweet spot is identified, the horizontal well is drilled and completed in that location to maximize the production of oil and gas from the reservoir. By targeting the sweet spot, the horizontal well can access the most productive part of the reservoir, leading to higher production rates and better overall performance.

The spacing between wells can have a significant impact on their productivity in a horizontal well field. The optimum spacing between horizontal wells depends on several factors, including the reservoir properties, formation type, and the production strategy.

If the wells are spaced too closely, they can interfere with each other's production and result in lower overall productivity. This can happen if the wells drain the same part of the reservoir, leading to a pressure drop in that area. This phenomenon is known as well interference or well communication. In this case, the production from each well can be reduced, and the overall recovery of oil and gas can be lower than expected.

On the other hand, if the wells are spaced too far apart, the reservoir between the wells may not be effectively drained, resulting in lower overall recovery. The optimum spacing depends on the reservoir characteristics such as porosity, permeability, and oil saturation, as well as the production strategy employed.

Reservoir engineers use analytical and numerical models to determine the optimum well spacing for a given reservoir. They can use production data from nearby wells to calibrate their models and predict the production rates from the new wells. In general, the optimum spacing between horizontal wells is determined based on maximizing the overall recovery of oil and gas from the reservoir while minimizing the risk of well interference.

Stimulation treatments are designed to increase the permeability of the formation and improve the productivity of the well. Stimulation treatments can include hydraulic fracturing, acidizing, and other methods that are intended to enhance the flow of oil and gas from the reservoir into the wellbore.

Hydraulic fracturing is a stimulation treatment that involves injecting water, sand, and chemicals at high pressure into the reservoir to create fractures in the rock. These fractures allow oil and gas to flow more easily into the wellbore, increasing the overall productivity of the well.

Acidizing is another stimulation treatment that involves the use of acid to dissolve the rock and create channels for oil and gas to flow through. Acidizing can be used to treat carbonate formations, which are often highly permeable but can become clogged with mineral deposits over time.

Other stimulation treatments include gas injection, which involves injecting gas into the reservoir to enhance the flow of oil and gas, and thermal stimulation, which involves heating the reservoir to reduce the viscosity of the oil and increase its mobility.

Overall, stimulation treatments are an important tool for increasing the permeability of the formation and improving the productivity of horizontal wells. Reservoir engineers carefully design stimulation treatments to ensure that they are effective and do not cause any negative impacts on the well or the surrounding environment.

Effective production strategies are essential for maximizing the recovery of oil and gas from horizontal wells. Here are some of the strategies used by reservoir engineers to increase recovery:

1. Reservoir management: Effective reservoir management involves monitoring the performance of the well and adjusting the production strategy as necessary. Reservoir engineers use production data, well tests, and modeling tools to optimize the production rate, injection rate, and well spacing to maximize recovery.
2. Enhanced oil recovery (EOR) methods: EOR methods are techniques used to recover oil and gas that is not produced by traditional production methods. EOR methods include gas injection, water flooding, and thermal methods such as steam flooding. These techniques are used to increase the sweep efficiency of the reservoir and push more oil and gas towards the wellbore.
3. Proper well completion: Proper well completion is critical to ensuring maximum production. Reservoir engineers design and implement well completion strategies that are optimized for the specific reservoir characteristics. This includes selecting the appropriate type of completion (e.g., open hole, cased hole), designing the completion to minimize skin damage, and optimizing the perforation strategy.
4. Stimulation treatments: As mentioned earlier, stimulation treatments such as hydraulic fracturing and acidizing can significantly increase the productivity of a well. Reservoir engineers use these treatments strategically to enhance the permeability of the formation and improve the flow of oil and gas into the wellbore.
5. Artificial lift: Artificial lift methods, such as electric submersible pumps (ESPs) or rod pumps, are used to increase the flow rate of oil and gas from the wellbore. These methods are particularly useful in wells that have low reservoir pressure or high viscosity oil.

Overall, maximizing the recovery of oil and gas from horizontal wells requires a comprehensive and strategic approach that considers reservoir properties, production techniques, and well design. Reservoir engineers carefully analyze the reservoir and implement effective production strategies to achieve the highest possible recovery rates.

Conclusions. Optimizing the productivity of horizontal wells requires careful consideration of several factors, including reservoir properties, completion techniques, and production strategies. Here are some key strategies that can be employed to maximize the productivity of horizontal wells:

1. Select the right completion technique: The choice of completion technique can have a significant impact on the productivity of horizontal wells. For example, the use of hydraulic fracturing can significantly improve the productivity of wells in low-permeability reservoirs, while open-hole completions can be more effective in high-permeability reservoirs.
2. Locate the wellbore in the sweet spot: The sweet spot is the region of the reservoir with the highest oil and gas saturation. Locating the wellbore in this region can significantly improve the productivity of horizontal wells.
3. Optimize well spacing: The spacing between wells can have a significant impact on their productivity. Optimum well spacing can be determined based on reservoir properties and production strategies.
4. Implement effective stimulation treatments: Stimulation treatments such as acidizing and hydraulic fracturing can significantly improve the productivity of horizontal wells by increasing the permeability of the formation.
5. Implement effective production strategies: Production strategies such as choke management and artificial lift can be used to optimize the flow rate and maximize the recovery of oil and gas.

References:

1. Al-Kaabi, A. H., & Nasr-El-Din, H. A. (2017). Optimization of horizontal well performance in unconventional reservoirs. Journal of Petroleum Science and Engineering, 157, 942–957. https://doi.org/10.1016/j.petrol.2017.09.006.

2. Miskimins, J. L., Vargas, F. M., & Rodriguez, A. (2003). The effects of formation damage on the productivity of horizontal wells. SPE Production & Facilities, 18(3), 173–180. https://doi.org/10.2118/80154-PA.

3. Ozkan, E., & Raghavan, R. (1991). Analysis of horizontal wells in naturally fractured reservoirs. SPE Reservoir Engineering, 6(2), 219–226. https://doi.org/10.2118/19277-PA.

4. Zhang, W., Wang, J., & Wu, Q. (2017). A numerical study of the effects of reservoir properties and completion parameters on the performance of horizontal wells in tight sandstone reservoirs. Journal of Natural Gas Science and Engineering, 41, 84–97. https://doi.org/10.1016/j.jngse.2017.02.020.