Multidiscipline Approach, Advanced LWD Boost Multistage Fracturing in Romania
Authors: Cataraiani Rodica , Tudora Elena , Dzhaikiev Bekdaulet , Subbiah Surej Kumar , Nohut Omar Murat 
Published: February 2015

Technology Update

Since the start of production from the Lebada fields offshore Romania in 1987, operator Petrom tested various stimulation and completion measures to improve production from the fields’ low-permeability formations. However, by 2008, the company had not been able to achieve production of more than approximately 115 BOEPD per well. A new multidisciplinary approach to well design, combined with the implementation of advanced directional drilling, logging-while-drilling (LWD), and completion technologies, has now increased production per well to a peak of more than 1,000 BOEPD and to stabilized levels of up to 750 BOEPD.

Petrom is the largest oil and gas producer in southeastern Europe. It was Romania’s national oil company until privatized in 2004, when it became a member of the OMV Group. Romania has been producing oil since 1856, mostly from onshore reservoirs. Petrom currently produces approximately 32,000 BOEPD from its five commercial offshore fields in the Black Sea, approximately 18% of the company’s annual 66 million BOE production in Romania (2009 figures).

The Lebada Oil Fields

Petrom’s Lebada Est (East) and Lebada Vest (West) fields are in block Histria XVIII in the Black Sea. Lebada Est was discovered in 1978 and represented Romania’s first offshore production when it came onstream in 1987. It produces oil from Upper Cretaceous carbonate shelf deposits—micritic, sandy and chalky limestones—overlain by overpressured Oligocene shales. Average porosity is 15% to 20% and average permeability is 0.8 md. Microfractures and intergranular porosity connect zones with good porosity in mainly calcareous reservoir forma-tions. Lebada Vest was discovered in 1985, with first production occurring in 1993. It is characterized by the same calcareous formations as Lebada Est in the top part and more clastic turbiditic fan deposits toward the bottom. A gas cap is often present.

In 2008, Petrom reviewed technical proposals to increase production rates significantly, having achieved only very limited success until then with measures such as acid fracturing and hydraulic fracturing of older producers completed with cemented and perforated liners. It was concluded that high production would require long horizontal drain sections with good quality borehole to be drilled. Because the hydrocarbons lay within shelf deposits, horizontal continuation of reservoir properties could not be guaranteed. Thus, real-time petrophysical evaluation and well placement would be necessary.

Synthetic oil-based mud (SOBM) would be beneficial to handle the Oligocene overpressured shale overburden, provide a better quality hole, and enable safe drilling, helping to ensure efficient, effective completions run along the reservoir section. However, this could limit the choice of formation evaluation logging tools. The low-permeability reservoir rock required hydraulic fracturing and fast, efficient, postdrilling reservoir characterization and natural open fracture detection to select the best locations for placing completion packers and ports.