Multiwell Production Allocation via Petroleum Fingerprinting: A Case Study in the Norwegian Sea
Authors:   Geolog Technologies, Franco Placido , Galimberti Roberto ,   Geolog Technologies, Garlichs Thorsten Uwe ,   Wintershall Dea Norge AS
Published: November 2024

Reservoir geochemistry is an established science that offers rapid, low-cost evaluation tools to aid in understanding development and production problems. In the last 30 years, thanks to significant advances in analytical chemistry and data processing, petroleum geochemical fingerprinting has allowed geochemists to carry out production allocation studies by mathematically unmixing a commingled oil fingerprint into the contributing flow inputs (endmembers). The present contribution deals with a successful pilot case study finalized to assess the applicability of geochemical production allocation to some production wells in an offshore field in the Norwegian Sea. The first phase of the study focused on a baseline assessment through endmember characterization. This process involved initial geochemical fingerprinting of the five contributing oil inputs to build a robust mixing model, which was also tested through analysis of synthetic laboratory mixtures. Subsequently, production samples were analyzed. The main challenge in this phase was individuated in the high oil similarity since production comes from a single target that shows only minimal molecular variations potentially able to contribute to the necessary geochemical differentiation across the field. Moreover, the relatively high number of wells to allocate and the proximity of some of them provided further elements of complexity. The selected analytical methodology employed for oil fingerprinting was based on gas chromatography-mass spectrometry (GC-MS) alkylbenzenes analysis, while fingerprint deconvolution was carried out using an original, in-house developed algorithm. The geochemical production allocation of several commingled oil samples resulted in a good agreement with existing multiphase flowmeter data, being the overall average discrepancy lower than 6%. The advantages of petroleum fingerprinting for production allocation have been extensively reported by many authors. Indeed, despite being relatively recent compared to more established techniques, the low cost, minimum impact on operations, and adaptability to many production programs led to the rapid diffusion of this allocation approach. The main limitation relies on the necessity to find significant compositional differences in the endmember oils that make up for the production, requiring carrying out a preliminary feasibility study. The results obtained from the present pilot study asserted the effectiveness of the proposed fingerprinting approach to allocate the production in the investigated area, standing as backup, calibration, and quality control to the used metering technique, as well as to provide further data for reservoir management. Petroleum fingerprinting allows us to directly analyze production streams, providing a rapid and inexpensive quantitative assessment of production allocation without requiring any production deferment. The reported pilot study proved the effectiveness of geochemical production in the studied area, historically metered by means of multiphase flowmeters, which are more expensive and not always accurate. More importantly, the present case study proves the methodology’s efficacy in a single-level multiwell production, which is a typical scenario where the proposed methodology generally presents applicability limitations.