Genetic susceptibility to multiple sclerosis (MS) is associated with genes of the major histocompatibility complex, particularly with the HLA DRB1*1501-DQA1*0102-DQB1*0602 haplotype in Caucasians. To investigate the association of DRB1, DQA1 and DQB1 alleles and haplotypes with MS in Biscay, Basque Country, northern Spain, we examined 197 patients and 200 regionally matched controls. High resolution HLA class II typing was performed by polymerase chain reaction followed by sequence-specific oligonucleotide probe hybridization. Several alleles were overrepresented in MS patients compared with those of controls: DRB1*0402, DRB1*1303, DRB1*1501, DQA1*0102, DQB1*0301, and DQB1*0602. DQB1*0602 was the only potentially predisposing allele for MS that withstood Bonferroni correction and maintained the association in a logistic regression model. On the other hand, several alleles showed lower frequencies in the MS group: DRB1*0101, DQA1*0101, DQB1*0303, and DQB1*0501, but only DRB1*0101 and DQB1*0303 maintained a negative association with the disease in the regression analysis. Three haplotypes were identified as potentially predisposing for MS in our population: DRB1*1501-DQA1*0102-DQB1*0602, DRB1*0402-DQA1*0301-DQB1*0302, and HLA-DRB1*013-DQA1*05-DQB1*0301. Additionally, three haplotypes associated with a lower risk for MS were identified, exhibiting DRB1*0101-DQA1*0101-DQB1*0501 the strongest negative association with MS [12% in controls vs. 3.8% in MS, Pc = 0.00047, OR = 0.290 (95% CI = 0.160–0.528)], and suggesting, therefore, a putative protective role for this haplotype in the population under study.
This work is the result of the authors' several experiences in sandy reservoirs of clay minerals matrix in the San Jorge Basin. It is intended to highlight the advantages of the use of integrated reservoir models originated from the group of ordinary lithologic characteristics among reservoirs, their integration to sedimentary subambients inferred from logs, and high technology log data (spectral gamma ray and magnetic resonance).
The majority of the reservoirs of the Bajo Barreal formation are volcanoclastic sandstones with porosities modified and/or reduced with burial and as diagenesis grades increase. That decrease mainly takes place due to three processes: mechanic compaction, dissolution of grains by intergranular contacts, and pore cementation.
The quantization of the compaction is influenced by the abundance and type of lithic material. The use of technologies that make it possible to have a detailed estimate of the lithology (Spectral Gamma Rays, Lateral Impact and Rotated Cores) is of pre-eminent importance when evaluating that type of reservoirs.
The diagenetic conditions and processes directly affect porosity determination from conventional logs. This justifies the use of porosity tools that are independent from the type of material of the reservoir rock. However, the combination of porosity data obtained in the NMR together with lithologic determinations and appropriate logs results into an interesting alternative to improve the evaluation of sandy reservoirs.
Generally, it is considered that volcanoclastic sandstones have a poor potential as oil reservoirs, because of their low porosity and permeability due to compactational processes and precipitation of authigenic mineral, such as cement. But thanks to the high reactivity of their materials with fluids from the reservoir, secondary important porosities are developed making the reservoir a high quality one. For this reason, these processes can be used to indicate the quality of volcanoclastic sandstones.
The implementation of methodologies, as the ones in this work, endeavors to apply evaluation criteria of sandy reservoirs.
Introduction
It is generally considered that volcanoclastic sandstones have a poor potential as oil reservoirs because of their poor porosity and permeability due to the action of diagenetic processes related to the sandstones burial. However, it is shown that some of these types of reservoirs develop secondary porosities which turn them into high quality potential reservoirs. For this reason, processes such as compaction, grain and cement dissolution are frequently used to determine the quality reservoir in volcanoclastic sandstones.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.