Porosity is the single most important petrophysical property. Knowing the porosity of the rocks(s) in an oil field is vital to the profitable development of the field. The porosity is reflective of the amount of oil present in a field. The earlier porosity is known, the earlier decisions can be made about how to best retrieve the oil from the field. Green Imaging Technologies has developed a method to acquire NMR porosity on drill cuttings allowing earlier information for decision making.
Rock core analysis and well logging are accurate techniques available for measuring petrophysical parameters (including porosity) in oil and gas reservoirs. However, well logging and coring are not done on all wells due to their high cost. These challenges make utilizing well bore cuttings a potential cost-effective method for porosity measurements as a function of depth in an oil or a gas well. However, modern drilling produces cuttings that are not suitable for most conventional porosity measurements as they are crushed into very small “grain- like” pieces.
Green Imaging Technologies has developed a new method to successfully measure cuttings porosity. The multi-step method is robust, fast and repeatableFortunately, nuclear magnetic resonance (NMR) measurements overcome the shortcomings of traditional porosity measurements allowing porosity to be determined efficiently and accurately on drill cuttings. However, NMR measurements of cuttings are not as straightforward as NMR analysis on rock cores. Determining the porosity of cuttings introduces a new set of challenges.
Surface water can hamper porosity determination because it can be misconstrued in the NMR measurement as water in the pores of the sample leading to an overestimate of porosity. Unfortunately, the method of simply displacing the surface fluid with a bathing fluid is not completely effective, especially when the cuttings have been drilled with polycrystalline diamond compact (PDC) drill bits which crush the rock to very small sizes. The smaller the cuttings, the more surface fluid there is per gram of cuttings making the effect of fluid on the surface even greater.
Green Imaging Technologies has developed a new method to successfully measure cuttings porosity. The multi-step method is robust, fast and repeatable and employs our knowledge of NMR, porous materials and laboratory techniques. As is shown in the figure on the left, our cuttings measurement correlates very well to NMR porosity measurements on plugs from the same zone.
SPWLA featured a webinar about GIT’s NMR cuttings measurement in June 2020 and it can be viewed here.