Craig Borman

Low Level Hydrogen Sulphide Detection using Wireline Formation Testers

Many development projects will rely on producing through existing production facilities, which may not have been designed for sour hydrogen sulphide (H2S) service. This problem is compounded if production is routed to an NGL or GTL facility because even a tiny amount of H2S may dictate a prohibitively expensive upgrade.

Systematic Evaluation of Asphaltene Formation Damage of Reservoir Fluids from Lake Maracaibo, Venezuela

One of the most concerning areas for asphaltene deposition is the near-wellbore region, where such deposition causes formation damage. The reservoir fluid of the Lake Maracaibo region is known to experience operational problems due to asphaltene deposition inducing production losses. A detailed asphaltene formation damage investigation was performed on the live oil samples from the Lake Maracaibo area. An unusual asphaltene precipitation envelop was observed for this fluid and reported in an earlier publication (Gonzales et al., SPE 153602, 2012). In the current paper, we focus on the systematic evaluation of asphaltene formation damage using stacked composite core samples. A special coreflood system was designed for an asphaltene formation damage study using reservoir core samples and sour–live reservoir fluid samples. The effect of flocculated asphaltene in the porous media was evaluated as the reservoir pressure decreases below the asphaltene onset pressure (AOP). Live samples were collected and flooded through the stacked composite core plugs under reservoir conditions. Progressive pressure reductions were performed to induce asphaltene precipitation in the porous media. Oil permeability changes were measured to evaluate the effect of this phenomenon in the reservoir using composite core. Significant impairment of composite core was caused by the depressurization of the reservoir fluid below AOP. The inlet pressures of the composite core stack were maintained just above AOP and the outlet pressure approximately 50 psi above saturation pressure throughout the core flood experiment. Thus, asphaltene precipitation onset occurred inside the composite core. This experiment showed significant permeability loss in the composite core after sufficient flooding of live oil fluid. Following the core flood experiment, the core stack was depressurized, and the remaining hydrocarbon was extracted from individual core plugs. Detailed chemical analyses were performed on the extracted hydrocarbon deposits from individual core plug with various analytical techniques, such as asphaltene content, simulated distillation, optical density, and thin-section analysis. These analyses’ results confirmed that the observed oil permeability loss was indeed due to the formation of asphaltene deposit inside the porous media, and the asphaltene deposition was somewhat more extensive in the tighter core sections.