fields_security/views/account_bank_statement.xml

<?xml version="1.0"?>
<openerp>
    <data>
        <record id="account_bank_statement_form_view" model="ir.ui.view">
            <field name="name">fields_security.account.bank.statement.form</field>
            <field name="model">account.bank.statement</field>
            <field name="inherit_id" ref="account.view_bank_statement_form2"/>
            <field name="groups_id" eval="[(6, 0, [ref('group_restrict_fields')])]"/>
            <field name="arch" type="xml">
                <field name="period_id" position="attributes">
                    <attribute name="invisible">1</attribute>
                </field>
            </field>
        </record>
    </data>
</openerp>