Lesson Learned: Fracturing Story Continues in Completely New Telisa Formation in B Structure South Sumatera
Authors: Alfajri R. 
Published: March 2023

Telisa is a formation in South Sumatera Basin that was famous for its hydraulic fracturing success. In 2020 Pertamina found Telisa as a new formation in B-Structure in well B-62, B-21, and B-20. The B-62 well can only produce intermittently in a space of two months. However, its water cut was as low as 50%. In order to produce the well continuously and increase its productivity, hydraulic fracturing treatment was planned. Since Telisa is considered soft rock with young modulus around 1 million psi, the treatment was designed to use 20/40 proppant to minimize embedment effect. According to petrophysical analysis this formation has 40 mD permeability, therefore treatment design was designed to be aggressive with fracture width as priority instead of half-length. After performing breakdown, step rate test, and data frac, it turned out that reservoir permeability is not as high as previously estimated in B-62 well. Transmissibility that was acquired from breakdown test data showed the value of around 8500 mD-ft/cp. Step down test, and was later confirmed by data frac, showed that this well has high entry friction at 1300 psi. Data frac showed presence of fissures, therefore fluid efficiency and pad ratio was adjusted accordingly to handle this non-ideal reservoir behavior. Final design was with total of 65,000 lbs 20/40 proppant with pre-treatment of hundred mesh sand slug to reduce entry friction. During main frac job, loss prime happened on one of the frac pumps that ultimately resulted in early screen out at the last proppant stage (7 ppg). Total proppant pumped into formation was 44,701 lbs. Investigation showed that there was foreign solid material that was accidentally pumped into the fracturing system. Lesson learned was taken from this well and implemented to the second well, B-21. There are several things to be considered: perforate formation with highest entry hole size available and increase gel viscosity to handle excessive entry friction, pump more sand slug to deal with fissures, and improve pumping system reliability by installing filter to prevent unwanted foreign solid material during pumping and performing horse power test to the frac pumps. With all of this preparation, B-21 fracturing was designed and executed. B-21 well has lower transmissibility value than B-62 well, which means this well has tighter formation. Unlike B-62 well, after closure analysis did not show non-ideal behavior. Operational mitigation was taken by installing filters on water tank, performing hydraulic horse power test to all of the fracturing pumps, and adding personnels during the job. For fracturing design, since entry friction was still around 1200 psi, sand slug was still used before 65,000 lbs 20/40 proppant. Even though mitigations have been taken as a precaution, this well was also suffered from early screen out at 6-7 ppg stage with total proppant pumped was 41,000 lbs. Evaluation on possible causes of early screen out from these two wells was taken in terms of design and execution. This evaluation would be a precious lesson learn for further development in B Structure Telisa Formation.