Abstract
Pertamina Hulu Sanga-Sanga is operator of Sanga-Sanga block located onshore of the Mahakam Delta, East Kalimantan Indonesia that has been producing since 1970's. With recovery factor to date is approximately of 70% of its initial in place, hence Sanga-Sanga block has entered maturity. However much of remaining reserve is still locked in reservoir with lower permeability where conventional completion cannot economically produce these type reservoirs. Many technologies have been applied in order to produce at economical rate these reservoirs, including hydraulic fracturing.
Hydraulic fracturing has been applied in Sanga-Sanga since 1980 until 2005 as first campaign but faced with many failures amounting 85% of the job failed. After a thorough study in 2006, one of the finding of contribution of failed job is high fracturing pressure triggered by high frac gradient. The study suggests that hydraulic fracturing reservoirs candidates should go through depletion to lower the pore pressure and lowering the frac gradient in process. By applying this method the second campaign had been executed from 2007 until 2012 with varying results.
Several failed jobs were identified as result of inability of the well to recover most of frac fluid in formation due to reservoirs have been very depleted with pore pressure below 2.5 Ppg. From this finding it is deemed that reservoirs with pore pressure less than 2.5 Ppg are not suitable as hydraulic fracturing candidates and therefore losing opportunity in producing depleted reservoirs.
In 2015 another attempt on executing hydraulic fracturing in depleted reservoir (pore pressure of 1.89 Ppg) was done. By addressing fracturing design, fracturing execution and sand clean out and Nitrogen (N2) unloading post hydraulic fracturing job resulted in successful job. The result was well was able to increase its production by 4 fold.
This paper illustrates the approaches in hydraulic fracturing in low pore pressure reservoirs (less than 2.5 Ppg) that usually are excluded as hydraulic fracturing candidates. This paper also discusses the challenges in hydraulic fracturing that comes with the typical reservoir characteristic in Sanga-Sanga and solution addressed in overcoming these challenges to achieve the successful hydraulic fracturing job especially in low pore pressure reservoirs.
