Full Life Cycle of Heavy Oil Development from Discovery to End State Thermal Recovery Steam Flood
Authors: Silalahi Henri Sahat , Nuruddin Mukhammad , Sucitra Anak Agung Hendra , Sofyan Anang 
Published: April 2024

Abstract
The Heavy Oil production plays a significant role in Indonesian energy supply. D Field contributes 12% of the world's heavy oil reserves and 8% of national oil production. It covers around 20,000-acre area and is discovered in 1941. It has more than 5 billion barrels of oil in place and achieved its first production in 1958. The D field composed of three main reservoir groups, B, CD and EFG reservoirs and confined with three-way closure structure with 17 km in length and 9 km in width. The D field has been recording a full cycle of steam flood development that reveals a lookback of implementation design development, technical aspect operation and impact of strategic decision.
The success of D Fields development is by applied steamflood methods and continues learning in each of development stages. The steamflood design and execution plan were built from subsurface simulation study and learning from pilot area that recommended the 11.6 acre-7 spots design and single sand target. The actual steamflood design was executed with 11.6 acre-7 spots, 15.5acre-9 spots, 5.5 acre-7 spots, and 3.87 acre-5 spots; commingle injection and production. These decisions introduce variation on outcome performance and operation challenge. First, the recovery aspect of the 11.6 acre-7 spots, 15.5acre-9 spots, 5.5 acre-7 spots, consecutively shows 50%, 47%, 60% in 10 years and URF 79.8%, 66% and 85%. Secondly, the heating of 5.5 acre-7 spot, 11.6 acre-7, 15.5acre-9 spot sequentially reached peak temperature in 6 years (highest injection rate), 8-years (lower injection rate) and 10 years (lowest injection rate). Third, the production and sweep efficiency of 5.5 acre-7 spots, 11.6 acre-7 spots, 15.5acre-9 spots, sequentially, reached highest peak within 2.8 years, short plateau production and 25-33% decline rate; moderate peak within 4.3 years, longest plateau production and 8-12% decline rate; moderate peak within 3.8 years, short plateau production and 15-22% decline rate. The large 15.5 acre-9 spot design causes an uneven sweep, in-efficient steamflood and bypass cold oil. The application relative uniform pattern design to entire reservoir quality ranges in early development resulting underperformed steamflood on some area.
A combinable pattern size reduction, pattern realignment, infill program and horizontal well was implemented to address the underperformed steam flood and bypass opportunity. The smaller pattern 5.5 acre-7 spot and 3.86 acre-5 spot with single target introduced to unlock bypassed oil in lower quality and higher pressure area. The infill well in large15.5-acre pattern aims to accelerate pressure drop and heating and horizontal well aims to sweep the single sand zone bypass oil.
This paper documented specific 40+ years of steam flood development journey in D field and provides recommendation mitigation on steamflood operation challenges. It explains the subsurface aspect of steam flood development design as well as recorded challenges and trade off economical decision. The actual development recorded the deviation in early development along staging area development impacted the later production performance and cost. The continuous learning during steamflood heat management and drainage process drives the proper mitigation to overcome underperformed steamflood and operational challenges.