The Stress Contrast Effect of Laminated Shaly-Sand Reservoir to Multistage Hydraulic Fracturing Design for Optimizing the Horizontal Well Productivity in K Field BACHELOR THESIS Kevin Joshua Reynaldi 12215037 Submitted as partial fulfillment of the requirements for the degree of BACHELOR OF ENGINEERING in Petroleum Engineering Study Program PETROLEUM ENGINEERING STUDY PROGRAM FACULTY OF MINING AND PETROLEUM ENGINEERING INSTITUT TEKNOLOGI BANDUNG 2019

The Stress Contrast Effect of Laminated Shaly-Sand Reservoir to Multistage Hydraulic Fracturing Design for Optimizing the Horizontal Well Productivity in K Field BACHELOR THESIS Kevin Joshua Reynaldi 12215037 Submitted as partial fulfillment of the requirements for the degree of BACHELOR OF ENGINEERING in Petroleum Engineering Study Program Approved by: Thesis Adviser, Zuher Syihab, S.T., Ph.D. NIP. 19720606 199903 1003
1 The Stress Contrast Effect of Laminated Shaly-Sand Reservoir to Multistage Hydraulic Fracturing Design for Optimizing the Horizontal Well Productivity in K Field Kevin Joshua Reynaldi*, Zuher Syihab**, and Farasdaq Muchibbus Sajjad*** Copyright 2019, Institut Teknologi Bandung Abstract The mature field K has been produced since 1986 and is characterized by heterogeneous reservoir formations. K-1 is one of the formations that is considered to be developed further by the operator company. Based on well logging analysis, K-1 consisted of sandstone formation with low resistivity and low permeability. However, according to petrography analysis, it was confirmed that the formation rock was sandstone dominated with shale layered-thin section. With the existing three production wells, the cumulative production from formation K-1 can only cover the ultimate recovery up to 3% of the total hydrocarbon in place. To increase the recovery of this formation, horizontal well with multistage hydraulic fracturing method was considered to be applied in this shaly-sand reservoir. The main challenge to perform horizontal well hydraulic fracturing is to make sure the fracture propagation can bypass the vertical permeability barrier by shale layers in the reservoir to be able to enhance the recovery throughout all layers. This challenge is dominantly bounded by the stress-contrast property between shale and sand layers that will mainly affect the propagation of fracture. Thus, the stress-contrast property should be well considered during the hydraulic fracturing design to be able to create fractures with the desired geometry. This study will show that the design that put consent on stress contrast will have an increase in dimensionless conductivity and significant increase in effective permeability and oil rate. The other parameter contributing to fracture propagation during hydraulic fracturing is the connection between fractures during the growth. One fracture growth can restrict the other fracture growth and lead to early screen- out, resulting in a non-optimum vertical growth. Therefore, hydrajetting will be overlooked as it will help preventing the overlaying fracture propagation and generate the result which is 4 times longer fracture height compared to common multislot operation. This paper provides a comprehensive study in designing the horizontal well multistage hydraulic fracturing with consideration to the stress-contrast property of shaly-sand layers. Multistage hydraulic fracturing is proven to be the optimum development scenario based on technical and economical evaluation for maximizing recovery of reservoir K-1. This scenario generates best drainage performance as lateral drainage is improved accordingly with bypassed vertical permeability barrier, which recovery attained is 37.96% improvement from current deviated fractured well existing. Moreover, multistage hydraulic fracturing gives highest IRR, biggest NPV for contractor and government, fastest payout time, and most interesting value of profitability index. Keywords: shaly-sand reservoir, stress-contrast, multistage, horizontal well multistage hydraulic fracturing Sari Lapangan K, salah satu lapangan dengan tingkat heterogenitas yang tinggi ini sudah diproduksikan sejak tahun 1986 dan sekarang dapat dikategorikan sebagai lapangan yang sudah tua. Reservoir K-1 memiliki karakteristik sebagai formasi batuan pasir dengan nilai resistivitas batuan dan permeabilitas yang rendah berdasarkan hasil interpretasi logging. Namun dengan menggunakan analisis petrografi, reservoir K-1 dikonfirmasi memiliki dominasi batuan pasir dimana terdapat lapisan-lapisan tipis dari batuan shale. Berdasarkan produksi dari 3 sumur yang ada, produksi kumulatif dari reservoir K-1 hanya dapat mencapai 3% nilai perolehan maksimum dari total cadangan. Inefesiensi dari skenario pengembangan reservoir saat ini pada akhirnya memotivasi studi lanjut untuk pengembangan menggunakan sumur horisontal dengan metode perekahan batuan hidrolik multi-tahap sebagai salah satu opsi untuk memaksimalkan perolehan dari reservoir shaly-sand ini.
2 Tantangan utama dalam melakukan metode perekahan batuan hidrolik pada sumur horisontal adalah memastikan propagasi dari rekahan dapat melewat hambatan permeabilitas rendah arah vertikal dari lapisan shale di dalam reservoir sehingga dapat meningkatkan perolehan minyak dari semua lapisan. Tantangan ini biasanya dipengaruhi oleh kekontrasan properti stress antara lapisan shale dan sand yang akan mempengaruhi propagasi dari rekahan yang terbentuk. Maka dari itu, properti stress yang kontras harus dikonsiderasi dalam mendesain metode perekahan batuan hidrolik sehingga dapat menghasilkan rekahan dengan geometri yang diinginkan. Hasil dari studi menunjukkan bahwa desain hydraulic fracturing yang mempertimbangkan kekontrasan stress akan memberikan fracture yang lebih konduktif dan juga memberikan peningkatan pada permeabilitas efektif dan laju alir minyak. Parameter lain yang mempengaruhi propagasi rekah ketika perekahan batuan hidrolik adalah koneksi antar rekah saat proses pertumbuhan. Pertumbuhan rekah yang satu dapat membatasi pertumbuhan rekah yang lain sehingga menyebabkan proses screen-out yang lebih cepat, dan kemudian menghasilkan pertumbuhan rekah vertikal yang tidak optimum. Untuk itu, hasil teknologi hydrajetting dalam perekahan multitahap akan dianalisa sebagai upaya preventif untuk menghindari restriksi selama propagasi rekah dan hasil analisa menunjukkan bahwa panjang fracture yang terbentuk 4 kali lebih panjang dari fracture yang biasa terbentuk pada operasi fracturing melalui multislot. Studi ini memberikan analisis komprehensif dalam mendesain metode perekahan batuan hidrolik multi-tahap pada sumur horisontal dengan mengkonsiderasi properti kontras stress dari lapisan shale dan sand sehingga dapat mendukung evaluasi teknis dan keekonomian dan memberikan rekomendasi skenario pengembangan yang optimum untuk memaksimalkan perolehan dari reservoir K-1. Skenario ini memberikan performa produksi reservoir yang paling baik dimana pengurasan arah lateral ditingkatkan melalui keberadaan sumur horisontal dan restriksi permeabilitas vertikal yang juga teratasi dari terbentuknya stress, sehingga memberikan peningkatan 37.96% perolehan minyak dari metode sebelumnya. Selain itu, perekahan batuan hidrolik multitahap juga memberikan hasil keekonomian yang paling baik dari parameter IRR, NPV kontraktor dan pemerintah, payout time, serta indeks profit. Kata kunci: reservoir shaly-sand, properti kontras stress, multistage, sumur horizontal dengan metode perekahan batuan hidrolik multitahap *) Student of Petroleum Engineering Study Program, Institut Teknologi Bandung, 2015 batch **) Thesis Adviser in Petroleum Engineering Study Program, Institut Teknologi Bandung ***) Thesis Adviser from Pertamina Hulu Energi Offshore North-West Java 1.
Introduction K-1 reservoir is categorized as a sand-dominated reservoir having a distribution of shale in thin laminated layers. The shale lamination is indicated by low resistivity and low permeability property from basic logging interpretation. Advanced petrography evaluation was then performed to provide greater understanding about the characteristic of this reservoir formation, especially in proving the low resistivity and permeability causes. X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) test were able to confirm the existence of significant shale in the form of lamination on this reservoir. Instead of having big reserves of around 30 MMBBL of oil, K-1 reservoir formation is suspected for being underdeveloped as the pressure monitoring shows slight reservoir pressure depletion and production history data shows insignificant recovery. By 2013, three development wells have been drilled and has been producing up to 2019, averaging current oil production of only around 100 bopd. Several symptoms have been defined, such as the reservoir is having low permeability value. Deviated well fracturing then was performed in 2013 for K-1A well, yet still contributing an insignificant production. Distribution of shale in form of lamination is then believed to be the main cause. This may create vertical permeability barrier and promote drainage inefficiency. Based on Fig. 1, connection between efficient porosity may be blocked due to existence of shale lamination that extends laterally. Thus, horizontal permeability hydraulic fracturing becomes the main focus on this study to enhance productivity of K-1 reservoir. Vertical fractures generated from horizontal well hydraulic fracturing operation may be able to bypass permeability barrier of shale lamination and enhance drainage efficiency for this reservoir. This operation will have significant effect to productivity if only the fractures created are able to extend and propagate throughout all layers. The design of hydraulic fracturing becomes the main control to ensure propagation is sustained.