The Identification of Calcium Naphthenates in a Heavy Oil Reservoir Using Laboratory Techniques to Assess Solids and Fluid Samples

Abstract

Abstract The precipitation of a black, hard scale initially described as coked asphaltene began to occur in a heavy oil reservoir in Bakersfield, CA. The material had never been encountered before, and previously developed analytical techniques were not providing hard answers as to the composition of the materials. Traditional chemistries applied to remediate asphaltic materials were completely ineffective, as were mineral and organic based acids. The initial samples gathered were somewhat soluble in traditional asphaltene dispersants, and initial applications of those products did yield some favorable results, but only for a short period of time. Several of the wells failed due to the same precipitates as before which seemed to get more tenacious with each subsequent failure. As more wells began to present with this material, it was apparent that the material being observed was not something previously found in the San Joaquin Valley (SJV). Analysis using X- ray diffraction (XRD) and X-ray fluorescence (XRF) yielded results that indicated that the material was primarily organic even though the deposits gathered indicated a very hard scale. Carbon, Hydrogen, and Nitrogen (C,H,N) analysis also provided data inconsistent with the known precipitates in the SJV. Wet Analysis techniques were altered to investigate synergies between chemical types and additional laboratory analysis were conducted to identify the Total Acid Number (TAN) and Specific Carboxylic Acid Number (SCAN™) of the produced fluids. The laboratory and analytical testing was able to establish several key findings. First of all, the TAN and SCAN data for the affected wells concluded that the material being precipitated was low molecular weight Calcium Naphthenate scale. The wet analysis in the laboratory identified combinations of treatment products that were effective at solubilizing the material. This was an important find because those same products applied as stand-alone treatments were not effective at solubilizing the material, but when combined; were able to return the material to solution. The ongoing investigations also determined thatthe material became more insoluble with aging, indicating that a prompt response to the occurrence could make the difference in a successful chemical application. This paper provides an important awareness of previously unknown deposits that may occur in producing wells that may not be common to many areas domestically as most of the work published on the subject is from the North Sea, Norway, Great Britain, Western Australia, Bohai Bay, offshore Trinidad, Lousiana, the Gulf of Mexico, China, and Africa (Baugh et al. 2005; Runham & Smith 2009; Shepherd et al. 2006; Turner & Smith 2005; Vindstad et al. 2003).