API RP 87:2007 pdf download
API RP 87:2007 pdf download.Recommended Practice for Field Analysis of Crude Oil Samples Containing from Two to Fifty Percent Water by Volume.
Alternatively, for spot sampling locations in horizontal pipes or where no specific mixing elements are used, it is recommended that these locations be confirmed as providing adequate results during the water injection tests as described in 5.1.1.
As an exception to the provisions above, well test or other related spot samples taken directly from a test well riser or other piping located directly downstream of a choke are typically well mixed (without a mixer) and shouki also be representative, provided a probe is installed and that. wi the case of a test separator, the test separator is operated in two-phase mode. However, for cases of three-phase test separators, it is normally better to meter the water outflow and sample/analyze the od outflow Ii order to determine the total produced water of the well.
A full open ball valve should be installed with /4 in. to 3/ in. (6 mm to 10 mm) tubing which should be continually sloped and without kinks, loops, high or low spots or fittings where water could accumulate. Spot samples shall be taken only after entire sample tubing has been purged at least once.
6 Sample Handling and Mixing
6.1 Sample Handling
Unless an aliquot Is delivered directly into the analytical glassware such as from the sample container mixing system or a spot sample probe, the entire sample must be analyzed In order to obtain accurate (unbiased) water content. This Is because the water portion of the sample will separate In the caplure/transter container very quickly. The result Is a disproportionate amount of the water at the bottom of the sample container which precludes the sub-sampling operation.
If samples must be taken using containers too large to analyze In their entirety (for example, for transportation to shore based or offshorelield laboratories), a circulating laboratory mixing system is required. When the sample arrives at the laboratory and has separated into two phases (Oil and water) the entire sample must be re-mixed and a sub-sane analysis may be performed.
Alternatively, after measuring the total volume of the entire sample, the free water may be removed from the oil phase and volumetrically measured. Subsequently, the residual oil phase will be ren’iixed, sub-sampled, and analyzed for water content. The water content of the oil-phase and the free water volume will be mathematically conined to determine the overall water content.
Spot samples may be taken &rectty into the analytical glassware (such as centrifuge tubes or graduated cylinders whereby the entire amount is analyzed). Likewise an aliquof may be taken directly from an automatic sampler mixing system into glassware. In these cases the analysis of the contents ol the assware is generally considered valid for the stream or the entire contents of the automatic sampler.
6.2 Laboratory Sample Mixing Procedure
Based on industry observation, the use of a high speed (13,000 rpm to 22.000 rpm) shearing mixing device inserted into a cylinder or jar is not considered to be an adequate mixing device for high water content samples greater than about one liter. Stirring or agitation of the separated samples will not adequately mix the contents for aliquot subsampling. Therefore, it is recommended that a lab mixing system of the following design be used:
— 1 gal to 5 gal (4 L to 20 L) sarr4e container size.
— A variable speed pump (speed based on viscosity/volume/density).
— Circulating tubing of 0.5 in, (12 mm) diameter with a static mixer,
b) Distillation method (ASTM D 95) with standard,200 mL crude oil sample and 20 mL trap with pet cock drain. Thetests conducted as a basis for this RP demonstrated that large amounts of water in the sample caused violent bilingproblems with subsequent condenser eruption.
c) Pre-separation graduated cylinder method of determining water content of the remaining oil phase by ditillation(API MPMS 10.2iASTM D 4006) or Karl Fischer titration. This method was abandoned due to inherent problems inobtaining a representative aliquot sample from the larger oil phase sample.
d) Reduced sample size centrifuge tests (API MPMS 10.3/ASTM D 4007) with the intent to increase the resolutionthrough readability of scale (oilwater interface readings in the conical section for better resolution). This method wasabandoned since results were better using the volume specified in the standard centrifuge test method.
