Introduction

In the coming decades, the reuse of water supplies is considered as the essential phenomenon which would alleviate the water demand challenges like environmental contamination by the hazardous materials in the produced water (Hagström et al. 2016; Smith et al. 2018). As a result, the adequate and sustainable supplementary of required water for several industries especially drilling operations would be considered as a major issue (Hickenbottom et al. 2013; Smith et al. 2017). The utilized water was used to circulate the drilling fluid which caused to cool the drilling systems such as drilling bit. Therefore, appropriate determination of complex chemical materials which were in the solution with water might be the major environmental concerns of petroleum industries (Bagheri et al. 2018; Bolis et al. 2018; Garg et al. 2017a). Hydraulic fracturing processes regarding the horizontal lateral length and number of cracking steps are considered as the principal water consumptions (Vengosh et al. 2014). Another significant source of water consumption in petroleum industries is enhanced secondary and tertiary oil recovery techniques such as steam-assisted gravity drainage (SAGD), water flooding, and polymer flooding (Davarpanah 2018; Taylor 2018). The management’s options of produced water are contained onsite reusing systems (not common), surface water discharge, injection disposal wells, and evaporation pits (Adham et al. 2018; Ersahin et al. 2018; Yu et al. 2017). In the recent decades, conventional sewage treatment technique is considered as the efficient way in the purification and separation of waste materials from produced water (Crini et al. 2018; Zhan et al. 2018). In this technique, the suspended materials and large floating particles are removed by the primary screening. Since then, about 55–60% of suspended solids would be removed in the primary sedimentation stage and subsequently regarding the biodegradability of the suspended solids, biochemical oxygen demand (BOD) has decreased about 35–40%. Next, biological performances are usually entailed in the treatment processes. In this process, the suspension of microorganisms is utilized to eliminate the biodegradable organics (Hansen et al. 2018; Hussain et al. 2018).

Artificial intelligence (AI) techniques are considered as the novel models to simulate the complex systems to ease these systems and rules. AI methods have entailed genetic programming (GP) and automated neural network (ANN) techniques. The working procedure of ANN method was contained the input layer which is entailed the neurons number as same as the input numbers, the output layer which is consisted of a single output of volume of flow-back water in the system. The last parameter which is called a hidden layer that has contained some unknown neurons and it has set a wide range of training algorithms. Therefore, the selectivity of activation functions in the output and hidden layer is based on the training algorithms. To ensure the validity and accuracy of the proposed ANN method, the volume of balanced water, the volume of each particle and material which is separated in each stage, and the limitations and possibilities of the developed approach are considered to the model (Alizadeh et al. 2017; Garg et al. 2017b). To perform the genetic programming for the developed model has consisted of the following stages; (1) before the implementation of GP method some parameters such as nonlinear functions and arithmetic operations of the proposed model, a set of terminal data included of four inputs, volume of water saving, volume of the produced water, possibilities of the genetic operations and threshold error must be defined. (2) The first generation of proposed model which is produced by the mixture of terminal and functional elements randomly. (3) Structural risk minimization (SRM) issue is also based on the complexities of the model to compare with the experimental error techniques and validate the model. Control the performances of the proposed model versus stopping criterion (maximum number of running the program and threshold error). Integrated water resources management (henceforth; IWRM) is schematically depicted in Fig. 1 (Asdak and Munawir 2017).

Fig. 1
figure 1

Integrated water resources management planning cycle (Asdak and Munawir 2017)

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Although, accuracy of water treatment systems would play a significant role in the providing of required water in drilling performances and several studies have wide reported in literature to concentrated on the importance of these procedures, we tried to calculate the required water for waterflooding, polymer flooding and hydraulic fracturing operations and how much volume of fresh water was saved for the drilled wells in Pazanan oilfield in the Iranian’s oilfield during the years of 2001–2017. According to the results of this comprehensive study, the conventional treatment system was purified a proper value of treated water for each process that caused to virtually eliminate the vast expenditures of water supply from large distances. Therefore, it is of importance that appropriate treatment of produced water in the treatment system would be an essential issue to control the water scarcity due to the enormous demand for water supply for drilling industries.

Materials and methods

Rock and reservoir characteristics

Adequate measurement of reservoir and rock properties would play a significant role in the estimation of reservoir productivity. To provide a more reliable estimation which is adapted to the real operational performances, all the parameters are measured more than one time to obtain an average value. The porosity was measured by neutron logs, and the permeability was measured by production logging tools (Davarpanah et al. 2018). The average value of each parameter is shown in Table 1. Furthermore, the average value of oil production rate, gas production rate, and water cut is shown in Table 1.

Table 1 Rock and reservoir characteristics
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Water treatment

Water scarcity is considered as one of the main concerns of petroleum industries. As an example, providing the required water for the injectivity scenarios, and hydraulic fracturing is always a problem in upstream industries (Veil 2011). Therefore, petroleum industries have tried to find novel solutions for the efficient treatment of water to meet the needs of operational performances (Fig. 2). The water treatment techniques are being explained summarily in Table 2.

Fig. 2
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The process of water treatment system (Golestanbagh et al. 2016)

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Table 2 Water treatment techniques
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Results and discussion

Water flooding

Water flooding is one of the primary enhanced oil recovery techniques in shale oil layers. This technique is considered as one of the economic and preferred enhanced oil recovery techniques, and it has proposed the less serious impact on the environment (Moustafa and Shedid 2017). The studied oilfield was started to produce in the year 2001. Due to the oilfield evaluations which were obtained from the wells in the field, natural drive mechanisms would be able to provide a sustainable economic amount of oil and gas for 2 years up to 2003. By passing the productivity time, natural drive mechanisms were weakened, and production from the studied field was not profitable enough. In this situation, the administration of flooding performances was essentially required to improve the productivity of trapped reserve oil in the reservoir. Waterflooding processes were lasted about seven sequential years up to the year 2009. Since then, regarding the reduction of oil recovery, the secondary and tertiary techniques were played a substantial role in the oil recovery enhancement. Provide the required water for waterflooding performances is considered as the main issues of this process which should be taken into consideration. Due to the water scarcity in recent decades, water treatment and reuse it in the flooding performances is the main priority of drilling industries. To do this, total required water during this period was measured averagely according to the daily measurement of injected water in the surface. This total required water was calculated by Eq. 1 for each well separately.

$$\begin{aligned} & \mathop \sum \limits_{i = 2003}^{2009} (((({\text{injected water}})_{\text{Day1}} + \cdots + ({\text{injected water}})_{\text{Day365}} )_{i} \\ & + \cdots + ((({\text{injected water}})_{\text{Day1}} + \cdots + ({\text{injected water}})_{\text{Day365}} )_{i + 6} )) \\ \end{aligned} .$$
(1)

As can be seen in Eq. 1, the total required injected water for the sequential waterflooding was calculated, and it is defined that the volume of required water for each year and how much water should be provided. Equation 1 calculated the total required water for each well. All the measurements are in a million gallons for 7 years of waterflooding. The produced water on the surface should be treated properly in the treatment systems. The produced water might contain the injected water and aquifer water that included many hazardous materials such as heavy metals and pollution materials. Therefore, to reinject this produced water, it was necessary to treat it in the conventional treatment system. The produced water was sent to the treatment systems near the drilling wells to avoid the transferring expenditures. The volume of treated water which could be reinjected to the wells was calculated by Eq. 2 averagely. In this equation, the input water is related to the produced water in the surface, and the output water is related to the treated water after treatment processes.

$$\begin{aligned} & \mathop \sum \limits_{i = 2003}^{2009} ((((({\text{input water}} - {\text{output water}}))_{\text{Day1}} + \cdots + (({\text{input water}} - {\text{output water}}))_{\text{Day365}} )_{i} \\ & + \cdots + (((({\text{input wate}}r - {\text{output water}}))_{\text{Day1}} + \cdots + (({\text{input water}} - {\text{output water}}))_{\text{Day365}} )_{i + 6} )) \\ \end{aligned} .$$
(2)

Subsequently, the total percentage of saving fresh water which is required for the waterflooding processes are calculated according to Eq. 3. Furthermore, the volume of required water treated water and saving water during waterflooding is shown in Table 3.

Table 3 The volume of required water treated water and saving water during waterflooding
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$$({\text{Average treated water/(average required water}} - {\text{average treated water}}))*100$$
(3)

As can be seen in Table 3, total required water for the waterflooding processes was calculated about 56 million gallons that relatively 40 million gallons of this volume was provided by the treated water in the treatment system. Therefore, the average percentage of fresh water savings in all the oil wells was measured approximately 72%.

Polymer flooding

Due to the productivity reduction at the end of 2009, waterflooding was not considered as the efficient way of enhanced recovery technique. Therefore, among different recovery techniques, polymer flooding was chosen for the studied field (Salmo et al. 2017). Polymer flooding had started from 2010 up to 2016. The volume of required fresh water, treated water and saving water is calculated from Eq. 1–3, respectively. The volume of required water, treated water and saving water during waterflooding is shown in Table 4.

Table 4 The volume of required water, treated water and saving water during polymer flooding
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As can be seen in Table 4, total required water for the polymer flooding processes was calculated about 12 million gallons that relatively 8 million gallons of this volume was provided by the treated Water in the treatment system. Therefore, the average percentage of fresh water savings in all the oil wells was measured by approximately 70%.

Hydraulic fracturing

Hydraulic fracturing performances are one of the mechanical techniques of opening the dead-end pores or increase the length of existed cracks by the purpose of oil recovery enhancement. This method would prefer when the recovery techniques were not efficient enough to provide sufficient oil and gas production. The volume of required water, treated water and saving water is calculated from Eq. 1–3 respectively. The volume of required water, treated water and saving water during waterflooding is shown in Table 5.

Table 5 The volume of required water, treated water and saving water during hydraulic fracturing
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As can be seen in Table 5, total required water for the hydraulic fracturing processes was calculated to be about 55 million gallons of which relatively 47 million gallons of this volume was provided by the treated water in the treatment system. Therefore, the average percentage of fresh water savings in all the oil wells was measured approximately 84%. The required water for drilling performances is contained lubrication processes, cooling operations, and etc. which allocated a small volume of water than other consumed processing water. Subsequently, the total required water for waterflooding, polymer flooding, hydraulic fracturing, and drilling performances was calculated about 125 million gallons that relatively 96 million gallons of this volume was provided by the treated water in the treatment system. Therefore, the average percentage of fresh water savings in all the oil wells was measured approximately 69%. This water volume is explained in Table 6.

Table 6 Total required water for all the processes
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Conclusion

Water reuse in the unconventional oil shale reservoirs is considered as the principal issues of petroleum industries regarding the environmental aspects of hazardous materials in the produced water in the surface which needed to be treated in conventional treatment systems. In the studied oilfield, waterflooding, polymer flooding and, hydraulic fracturing performances were done sequentially from the year 2001 to 2017 in Pazanan oilfield. Subsequently, the fresh water saving was measured for waterflooding, polymer flooding, and hydraulic fracturing 71.5%, 70%, and 83.7%, respectively, which was illustrated that most of the injected water was treated again and reinjected in the fracturing operations. Moreover, the total volume of required water for drilling of these wells in Pazanan oilfield during 2001–2017 was relatively 125 million gallons that water treatment systems supplied about 95 million gallons of this volume. Consequently, the average volume of fresh water saving was relatively 70% which was clarified the accuracy of the treatment system in the separation and purification of wastewater.