Creating An Abstract Class That Will Define All Database Manipulation Methods To Implement

I am developing a couple of small ASP.NET application and would like to know what pattern. approach do you use in your projects.

My projects involve databases, using Data access and Business logic layers.

The data-access approach that I was using so far is the following(I read in some book and liked it):

For DAL layer:

Creating an abstract class that will define all database manipulation methods to implement.
The abstract class will contain a static "Instance" property, that will load (if instance == null) an instance (Activator.CreateInstance) of the needed type (a class that implements it).

Creating a classes that implement this abstract class, the implementation will be according to the databases (SQL, mySQL and etc) in use.

With this I can create different implementation according to database in use.

For BLL layer:

A class that encapsulates all all retrieved fields , and static methods that will call the DAL classes.