Net pay (NP) and net-to-gross ratio (NGR) are often crucial quantities to characterize a reservoir and assess the amount of hydrocarbons in place. Numerous methods in the industry have been developed to evaluate NP and NGR, depending on the intended purposes. These methods usually involve the use of cut-off values of one or more surrogate variables to discriminate non-reservoir from reservoir rocks. This study investigates statistical issues related to the selection of such cut-off values by considering the specific case of using porosity () as the surrogate. Four methods are applied to permeability-porosity datasets to estimate porosity cut-off values. All the methods assume that a permeability cut-off value has been previously determined and each method is based on minimizing the prediction error when particular assumptions are satisfied. The results show that delineating NP and evaluating NGR require different porosity cut-off values. In the case where porosity and the logarithm of permeability are joint normally distributed, NP delineation requires the use of the Y-on-X regression line to estimate the optimal porosity cut-off while the reduced major axis (RMA) line provides the optimal porosity cut-off value to evaluate NGR. Alternatives to RMA and regression lines are also investigated, such as discriminant analysis and a data-oriented method using a probabilistic analysis of the porosity-permeability crossplots. Joint normal datasets are generated to test the ability of the methods to predict accurately the optimal porosity cut-off value for sampled sub datasets. These different methods have been compared to one another on the basis of the bias, standard error and robustness of the estimates. A set of field data has been used from the Travis Peak formation to test the performance of the methods. The conclusions of the study have been confirmed when applied to field data: as long as the initial assumptions concerning the distribution of data are verified, it is recommended to use the Y-on-X regression line to delineate NP while either the RMA line or discriminant analysis should be used for evaluating NGR. In the case where the assumptions on data distribution are not verified, the quadrant method should be used.

Net pay (NP) and net-to-gross ratio (NGR) are often crucial quantities to characterize a reservoir and assess the amount of hydrocarbons in place. Numerous methods in the industry have been developed to evaluate NP and NGR, depending on the intended purposes. These methods usually involve the use of cut-off values of one or more surrogate variables to discriminate non-reservoir from reservoir rocks. This study investigates statistical issues related to the selection of such cut-off values by considering the specific case of using porosity () as the surrogate. Four methods are applied to permeability-porosity datasets to estimate porosity cut-off values. All the methods assume that a permeability cut-off value has been previously determined and each method is based on minimizing the prediction error when particular assumptions are satisfied. The results show that delineating NP and evaluating NGR require different porosity cut-off values. In the case where porosity and the logarithm of permeability are joint normally distributed, NP delineation requires the use of the Y-on-X regression line to estimate the optimal porosity cut-off while the reduced major axis (RMA) line provides the optimal porosity cut-off value to evaluate NGR. Alternatives to RMA and regression lines are also investigated, such as discriminant analysis and a data-oriented method using a probabilistic analysis of the porosity-permeability crossplots. Joint normal datasets are generated to test the ability of the methods to predict accurately the optimal porosity cut-off value for sampled sub datasets. These different methods have been compared to one another on the basis of the bias, standard error and robustness of the estimates. A set of field data has been used from the Travis Peak formation to test the performance of the methods. The conclusions of the study have been confirmed when applied to field data: as long as the initial assumptions concerning the distribution of data are verified, it is recommended to use the Y-on-X regression line to delineate NP while either the RMA line or discriminant analysis should be used for evaluating NGR. In the case where the assumptions on data distribution are not verified, the quadrant method should be used.

För att attrahera kompetent personal till högskatteländer finns behov att kunna tillförsäkra dem en viss disponibel inkomst. Avtal om nettolön har därför blivit en vanlig företeelse vid förflyttning av personal utomlands. Arbetsgivaren betalar då den inkomstskatt som belöper på arbetstagarens ersättning. Redan 1977 fastslog Regeringsrätten att nettolön måste räknas om till ett bruttobelopp innan den kan tas upp som skattepliktig intäkt. Hur själva beräkningen ska ske har varit föremål för meningsskiljaktigheter med avseende på huruvida skattemässiga avdrag ska tas med i beräkningen av bruttolönen eller endast dras av efter det att bruttolönen fastställts. Syftet med förevarande uppsats är därför att avgöra vilken beräkningsmetod som har stöd i nu gällande svensk rätt för beräkning av bruttolön vid nettolöneavtal. I avsaknad av en direkt reglering av beräkning av bruttolön utifrån ett nettobelopp sker tolkningen av gällande rätt i stor utsträckning efter praxis och doktrin. Dock tillmäts även skatterättsliga principer en avgörande betydelse då de utgör viktiga hjälpmedel för tolkning av skatterätt. En analys av rättskällorna ger dock stöd för olika slutsatser. Ett nyligen lämnat prejudikat från Regeringsrätten anger klart att avdrag inte ska beaktas vid bruttolöneberäkningen medan skatterättsliga principer, tidigare praxis och argumentation framförd i doktrin ger för handen att avdrag ska beaktas vid beräkningen. Författaren finner att Regeringsrättens domskäl saknar rättslig grund, varför det nya prejudikatet lämnas utan hänseende. Gällande rätt ger därmed stöd för en beräkningsmetod där skattemässiga avdrag beaktas vid omräkningen av nettolön till bruttolön. / To attract competent employees to work in countries where the tax burden is heavy there is a need to ensure them a disposable income. This has resulted in a common use of net pay agreements when moving personnel abroad, whereby the employer pays the income tax on the employee’s salary. In 1977 the Supreme Administrative Court of Sweden held that a net pay has to be recalculated into a gross salary before declared as taxable income. How this calculation should be made has been subject for controversy with regard to whether tax deductions should be considered when calculating the gross salary or just be deducted when the gross salary has been determined. The purpose of this thesis is to determine the method of calculation that is in accordance with Swedish law when calculating gross salary from a net pay agreement. Due to the lack of legislation that directly regulates calculation of gross salary from a net amount the interpretation of Swedish law to a large extent constitutes of guidance from case law and legal literature. Furthermore, fiscal principles are of great importance since they are fundamental for the interpretation of tax law. An analysis of the sources of law results in a finding of support for different conclusions. A recently pronounced precedent clearly states that tax deductions shall not be considered when calculating gross salary, while the fiscal principles, previous case law and arguments presented in legal literature support a method where tax deductions are taken into account. The author finds the Supreme Administrative Court´s grounds for the judgment to lack of legal basis; thus the precedent is disregarded. Therefore, a method where tax deductions are considered when recalculating a net pay into a gross salary is in accordance with Swedish law.